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Millennials: sickness presenteeism and its correlates: a cross-sectional online survey

Objective Sickness presenteeism (SP) is a well-documented phenomenon in the current workforce. However, little is known about the SP of future employees (Millennials). We investigated rate and propensity of presenteeism and health-related and work-related correlates in university students to obtain information about the relevance of SP in the future workforce. Sickness presenteeism (SP) refers to going towork while ill.1 Design and setting We administered a cross-sectional online survey in August 2018 involving self-assessments of health-related and work-related behaviour. As planned, we analysed rates, instances and propensities of presenteeism and absenteeism. The target population was Millennial university students. Results 749 German university students, average age 24.7±3.6 years, 49.5% women, mean academic progress 4.5±2.7 semesters, <1% without work experience, 15.4±10.3 mean weekly working hours. Presenteeism rates in the complete sample were 64% at school and 60.4% at work. For the subsample of participants who reported sickness, presenteeism rates were 87.9% at school and 87% at work. Presenteeism propensity among them was 0.67±0.34 at school and 0.68±0.35 at work. SP at school and at work was significantly correlated with subjective health (r=0.29, p=0.000 and r=0.25, p=0.000) and locus of control (r=−0.20, p=0.000 and r=−0.26, p=0.000). Age and sex adjusted multiple regression analysis showed that subjective health explained 9.7% of the variance in SP at school (B=0.049, p=0.000) and 8.1% of the variance in SP at work (B=0.037, p=0.000). Conclusions The SP rates of the future workforce were in line with previous research on older employees, whereas the presenteeism propensities we found here were higher. Across all analyses, subjective health proved to be associated with presenteeism. Thus, the relevance of SP will remain constant or might even increase with regard to the future workforce. Programmes offering health education should be implemented to sensitise this generation as early as possible.


Strengths and limitations of this study
• The first study to investigate sickness presenteeism among individuals constituting the future workforce (Millennials) • Analyses distinguish between individuals with health problems and those without • The study focuses on not only the presenteeism rate but also on presenteeism propensity • The cross-sectional data do not allow for causal conclusions • Data are based on self-assessments

Introduction
Sickness presenteeism (SP) refers to going to work while ill. 1 The study of SP has gained in importance during the past two decades due to its association with sickness absenteeism, productivity, health, and attitudes. 2 Although the vast majority of empirical studies of the phenomenon are cross-sectional surveys, 3  mental health, 7 and higher rates of future sickness absences. [8][9] In addition, factors associated with burnout, such as depersonalization, 10 11 emotional exhaustion, 10 and an increased risk for depression among initially non-depressed participants 12 have been reported. Other negative effects of SP for the individual are productivity loss 13 and a decline in work attitudes. 14 15 Considering effects for the employing organization, there is empirical evidence for uncovered costs caused by productivity loss. 16 SP has been reported independently of a variety of sociodemographic variables. These include gender, age, educational level, family status, and level of income. 1 17-23 Although physicians have been investigated relatively often, SP has been found in various kinds of professional groups, such as teachers, administrative employees, construction workers, medical staff, and the self-employed. 17 19 24-29 SP is a global phenomenon. Its prevalence has been documented in many countries in Europe, 17 25 29 30 the U.S., 31 Canada, 32 33 Asia, 34 and Arabia. 35 The presenteeism rates reported for study samples vary from 30% to more than 90%. However, studies usually do not differentiate between individuals suffering from health events who are thus able to show SP at all and individuals without health problems who per definition cannot show SP behavior. 36 Therefore, these studies provide information about the prevalence of SP in the workforce, however, not about the prevalence among sick employees. Due to the wide range of negative effects of SP for individuals and organizations as well as its global ubiquity, the study of SP seems advisable. Insights into the process and the outcomes of the phenomenon will be useful for individuals so that they can understand the impact of their behavior.
In addition, more information about the effects of SP will provide corporate human resource management and corporate health management with crucial information regarding the design of interventions to manage SP in their organizations. [37][38][39][40][41][42][43][44][45] Knowledge of SP is also relevant in the wider societal, economic, and political context because negative health effects and associated sick leave burden social systems such as the public health system; e.g., with regard to health insurance benefits. 46 47 Cumulative effects of presenteeism and absenteeism might also affect the national economy, 48 politics, and legislation pertaining to the continued payment of wages in the case of sick leave. 49 50 When studying SP, it is necessary to distinguish between SP rates and SP propensity. 51 SP rates are frequency measures of attending work while ill. They depend on the number of health events and are an indicator of health status or vulnerability to illness. 52 SP propensity is the percentage of days worked while ill over the total number of days of sickness, 32 and it reflects an individual's probability of opting for sickness presence rather than sickness absence in the case of illness. 52 Thus, it offers additional information with regard to the decision-making process of the individual.
However, although SP rates are well documented for the current workforce, the majority of which belong to the generations of Baby Boomers and Generation X, 53 54 empirical evidence concerning the SP behavior of the future generation of workers is scarce. 55 56 Current university students are predominantly classified as Millennials who are sometimes also called Digital Natives, 53 57 who are said to have different attitudes toward work than older generations. In particular, they have greater entrepreneurial interests, 58 and they adopt a "work-to-live" attitude with a higher priority on worklife balance 57 59 than former generations. Generally, interests and work values are relatively stable 54 and are associated with behavior. Thus, knowledge about the SP-related behaviors of current students will be useful in order to evaluate the significance and its consequences for individuals, organizations, and society in the future. In order to investigate current students' SP behavior and its association with other health-related variables, we conducted an online survey.

Study design and population
During the 2018 summer term, students from German institutions of higher education were invited to take part in an online survey on attitudes toward work-and health-related behavior via a circular e-mail. Participants were informed that the survey was anonymous and voluntary and that they could withdraw their participation at any time. Of the 1,291 individuals who began taking the online survey, 791 provided complete data.

Measures of presenteeism and absenteeism
Because many students do not only study full time but are also employed in paid part-time jobs to contribute to their living, we collected data on presenteeism and absenteeism separately for school and work. To measure SP frequency, students were asked how often during the past twelve months they went to classes although their health state would have justified staying home. 1 9 60 The same question was posed for going to work. While other studies have used fixed response categories such as "never," "once," "2 to 5 times," and "more than 5 times," 1 30 60 61 we used an open-question format. The reason for this was that the former is seen as too crude for such a low base rate behavior and might convey information about what is perceived as normal and thus bias the answers. 62 Sickness absence (SA) was also measured with two items asking students to indicate how often during the past twelve months they stayed home due to sickness instead of going to classes/work. two-sided p-value of less than 0.05 was considered statistically significant. We performed all analyses with SPSS 24.

Results
A total of 791 questionnaires were completed. In accordance with the goal of the study, the analyses were restricted to participants belonging to the generation of interest, the Millennials, which include people who were born in 1981 or later. 53 57 Further, cases of long-term absence or presence were excluded from the analyses because these were likely to have been caused by different modalities. 52 As was done in other studies, we defined 60 days as the threshold. 52  participants did not report any health event during the last twelve months during school time.
Concerning work days, 30.3% reported no health events. .32*** -22*** -.10* .24*** * <.05 / **<.01 / *** <.001 SP frequencies and rates. Referring to the complete sample, as is typical for the reporting of SP rates, 1 9 23 30 the descriptive values are reported in Table 2 (left side). For the further exploration of SP behavior and its correlates, the analyses were restricted to participants who reported at least one incident of sickness. The reason for this is that only individuals who reported some kind of illness during the past twelve months were able to show presenteeism (see Table 2, right side). As results show, 72.8% of the sample were left for analyses regarding SP at school (N=545) and 69.7% with regard to work (N=468). Therefore, after excluding "healthy" participants, the SP rates rose to 87.9% during school time and 87% during work time.  2.09 (3.34) Work time 682 60.4% 2.36 (4.32) 1.19 (2.38) 468 87% 3.41 (4.86) 1.69 (2.70) Thus, the difference between SP incidents and SA incidents during school time was significant (t(544)=7.819, p<.001). When experiencing illness during school time, 39.6% always chose to go to classes, whereas 12.1% never did. With regard to work, the pattern was quite similar: SP incidents during work time differed significantly from SA incidents (t(467)=7.620, p< 0.001). 41.9% always chose to go to work in spite of illness, and 13% never did.

Correlates of SP:
With regard to SP at school, we found a significant correlation with SP at work (r=.62, p<0.001). Further correlations for SP during school and work time are listed in Table 3. Table 3. Correlates of sickness presenteeism among the participants with incidents of sickness In order to investigate the two most important correlates further, we performed median splits for both: subjective health had a median of 35.5 (participants with values above were coded as high in subjective health), and locus of control had a median of 4.0 (participants with values above were coded as internal locus of control). Means and SDs are listed in Table 4. A two-way analysis of variance (ANOVA) of subjective health by locus of control revealed two significant main effects and no significant interaction. Presenteeism frequencies at school were significantly higher for participants with good subjective health in comparison with those with poor subjective health (F(1)=18. 13, p<.001). Further, participants with an external locus of control had significantly higher frequencies than those with an internal locus of control (F(1)=4.57, p<.05). The highest values were found for the additive effect of high subjective health and external locus of control.
The same pattern was found for presenteeism frequencies at work: They were significantly higher for participants with good subjective health in comparison with those with poor subjective health (F(1)=6. 30, p<.05). Further, participants with an external locus of control had significantly higher frequencies than those with an internal locus of control (F(1)=4. 63, p<.05). Presenteeism propensity. We computed presenteeism propensity as SP frequency divided by the number of health events for university and work settings separately. Hence, SA propensity was 1-SP propensity. 52 Presenteeism propensity, which reflects an individual's probability of opting for presenteeism instead of absenteeism when suffering a health event, was 0.67 (SD=0.34) at school and 0.68 (SD=0.35) at work. Presenteeism propensity at school was significantly associated with presenteeism propensity at work (r=.50, p<0.001). Of course, there were significant correlations between SP frequency and presenteeism propensity; however, because the formula for presenteeism propensity contains SP frequency, it would not be productive to report them.
The probability of going to classes when sick was significantly higher than the probability of staying home (t(544)=11.414, p<0.001). When experiencing sickness during school time, 39.6% always chose to go to classes, whereas 12.1% never did. With regard to work time, the pattern was quite similar: The probability of going to work while ill was significantly higher than the probability of staying home (t(467)=10.906, p<0.001). 41.9% always chose to go to work in spite of illness, and 13% never did.
There were no gender differences in presenteeism propensity during school or work time.

Discussion
While more than one fourth of participants reported no incidents of sickness during the past year, those who reported at least some kind of illness reported a larger number of days of sickness during school time than during work time. SP rates for the complete sample were 64.4% at school and 60% at work. However, the rates increased by more than 35-40% when referring only to those participants who were sick and thus able to show SP. Presenteeism propensities for school and work were identical. Propensities showed that on average, in 2 out of 3 cases, participants who were sick chose to attend class or go to work and thus showed significantly more SP than SA. A more detailed view of the data revealed that the proportion of participants who always decided for SP when they were sick was more than three times higher than those who always choose SA. SP at school and SP at work were highly correlated. Further, SP was positively associated with good subjective health and an external locus of control and negatively correlated with occupational self-efficacy. It is noteworthy that especially the combination of good subjective health with an external locus of control was associated with high levels of SP. One might assume that locus of control as a rather stable variable influences SP, whereas the direction of the influence between subjective health and SP is unclear.
Thus, because we applied a cross-sectional design, we cannot identify cause and effect. Another weakness of the study is that all measures were self-reports, and thus, their reliability might suffer from common method bias and overreporting due to social desirability. 62 In addition, as in many other studies, 3 participants were asked to recall incidents of sickness presence and absence over a one-year period, and therefore, the data might be biased by false recollection. 62 However, because the self-reported measure of days of sickness 68 and the subjective measure of health status 69 demonstrated a high level of correspondence with objective data, we used the self-report method as a practicable way to obtain the relevant data. Pertaining to the goal of the study to investigate SP among the generation of Millennials, a strength of the survey is that it provides information about the SP behavior of the future workforce, a group that has not yet been investigated with regard to SP. In addition, to our knowledge, the study is the first one to explore SP among students. However, it has to be noted that the current students are rather younger Millenials whereas the older ones within this generation are already in the labor market. Further, since many of the participants were not only studying but were also working part time, this study allowed us to assess SP behavior in university and work settings at the same time and to compare them. However, it is obvious that the sample was restricted to students and thus does not allow generalizations about manifestations of SP behavior among full-time employees in these birth cohorts.
Additional advantages of the study are that we calculated propensities and made a distinction between individuals with and without health problems. In most studies to date, participants have been asked to quantify the number of times they have engaged in SP but not the number of times  36 recommendation to separately identify the SP prevalence for the subsample of individuals who reported some kind of illness. In their study, SP rates of 23% for the complete sample more than doubled for those with health problems (53%). In our study, the difference was only about one third, but SP levels were much higher. The levels of 60.4% and 64% found here are in the same range as studies that were conducted with employees in the Netherlands 28 and Scandinavia 70 and other European countries. 23 Recent research among German employees reported great variability in rates ranging from 35% 71 to more than 90%. 70 Further, the proportion of more than a quarter of participants who reported no health event during the past year is higher than in other studies. 52 This higher rate might be due to the fact that the sample we investigated is younger than the usual workforce samples. To date, only a few studies have explored presenteeism propensities. 52 53 53 reported a propensity of .50 for Canadian employees, and Gerich (2016) 52 reported .59 for Austrian employees.
The propensities found in the current study among students seem to be slightly higher (.67 and .68).
This finding seems to contradict the Millennials' focus on work-life balance that has been reported for this generation. 57 59 The correlation of SP with subjective health status found here is well established. 62 However, there is only one earlier study we know of that investigated the relation between health locus of control and presenteeism. Johns (2011) 72 found lower SP for people with an internal health locus of control. Although we measured general locus of control, we found the same pattern, i.e. a higher SP rate for individuals with an external locus of control. In addition, we found that subjective health and locus of control together formed an indicator. Self-efficacy has been postulated to be associated with SP. 2 65 66 investigated effects of SP in a sample of Chinese full-time workers and found a positive correlation between SP and self-efficacy and also found that self-efficacy could buffer the negative effect of SP on health. In our study, we found a negative correlation between SP and occupational self-efficacy, indicating that participants with low occupational self-efficacy show higher levels of SP. The difference in findings might be because Lu et  Johns (2010) 62 suggested that a person's proclivity to take the sick role was a determinant of SP. In our study, however, this proclivity had hardly any value for the explanation of SP. Of course, this finding might be due to the way in which it was operationalized.
The high prevalence of SP among individuals who reported some kind of illness is in accordance with recent findings that SP prevalence is continuously rising, 73 which means the issue will remain an important one. Sickness presenteeism and the associated risks are not restricted to the current workforce but are prevalent among those who are currently enrolled in a university. One should think about implementing health education concerning SP for students who represent the future workforce and soon-to-be managers in order to sensitize them to the management of SP at an early stage. The distinction between SP rates for the complete sample and the subsample of those with health problems provides answers to two separate questions. On the one hand, SP prevalence among the complete sample indicates the economic significance of the problem. On the other hand, SP prevalence among workers with health issues provides HRM and corporate health management with relevant information as to how many employees need support and what kind of measures might be helpful. SP rates, or at least a combination of SP and SA, were previously shown to be better health indicators than SA alone . Therefore, both methods of calculation are useful; however, in terms of health interventions, it is more appropriate to consider the part of the workforce that reported some kind of illness

Author Contributions
Both authors worked on all parts of the study together.

Funding
This research received no specific grant from any funding agency in the public, commercial or notfor-profit sectors.

Conflicting interests
None declared.

Ethics approval
The study was ethically approved by the ethics commission of the German Society for Psychology (DGPs).

Informed consent
Participants gave informed consent before taking part in the survey and could withdraw their participation at any time.

Data statement
No additional data available.

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Millennials: Sickness presenteeism and its correlates -A cross-sectional online survey
Abstract Objective: Sickness presenteeism (SP) is a well-documented phenomenon in the current workforce.
However, little is known about the SP of future employees (Millennials). We investigated the rate and propensity of presenteeism as well as health-and work-related correlates in university students to obtain information about the relevance of SP in the future work force.
Design and setting: We administered a cross-sectional online survey in August 2018 involving selfassessments of health-and work-related behavior. As planned, we analyzed rates, instances, and propensities of presenteeism and absenteeism. The target population was Millennial university students.

Conclusions:
The SP rates of the future work force were in line with previous research on older employees, whereas the presenteeism propensities we found here were higher. Thus, the relevance of SP will remain constant or might even increase with regard to the future workforce. Programs offering health education should be implemented in order to sensitize this generation as early as possible.  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59 1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60   F  o  r  p  e  e  r  r  e  v  i  e  w  o  n  l  y  Introduction Sickness presenteeism (SP) refers to going to work while ill. 1 The study of SP has gained in importance during the past two decades due to its association with sickness absenteeism, productivity, health, and attitudes. 2 Although the vast majority of empirical studies of the phenomenon are cross-sectional surveys, 3 important consequences of presenteeism for the organization and the individual have been established in longitudinal research. Studies have reported negative effects for individual health. [4][5][6][7][8][9][10][11][12] Other negative effects of SP for the individual are productivity loss 13 and a decline in work attitudes. 14 15 Considering consequences for the employing organization, there is empirical evidence for uncovered costs caused by productivity loss. 16 SP has been reported independently of a variety of sociodemographic variables 1 17-23 and for various kinds of professional groups. 17 19 24-29 SP is a global phenomenon. Its prevalence has been documented in many countries in Europe, 17 25 29 30 the U.S., 31 Canada, 32 33 Asia, 34 and the Middle East. 35 The presenteeism rates reported for study samples vary from 30% to more than 90%.
Due to the wide range of negative effects of SP for individuals and organizations as well as the global ubiquity of SP, the study of SP seems advisable. However, although SP rates are well documented for the current workforce, the majority of which belong to the generations of Baby Boomers and Generation X, 36 37 empirical evidence concerning the SP behavior of the future generation of workers is scarce. [38][39][40] Matsushita and colleagues (2011) 39 developed an instrument to measure presenteeism among students, but they did not report on presenteeism behavior. Johansen (2018) 38 analyzed motives for the presenteeism of students in secondary school. To our knowledge, the study by   40 is the only one to date to investigate the presenteeism behavior of students. They did not find any differences in prevalence rates between medical students and STEM students and reported higher levels of presenteeism for female that for male students.
However, the prevalence rate they reported could not be compared with other studies because their way of measuring and aggregating presenteeism behavior was uncommon. Current university students are predominantly classified as Millennials, 36 41 who are said to have different attitudes  42 and they hold a "work-to-live" attitude with a higher priority on work-life balance 41 43 than previous generations. Especially this latter trend suggests that presenteeism among Millennials should be lower than among older generations. In general, interests and work values are relatively stable 37 and are associated with behavior. Thus, knowledge about the SP-related behaviors of current students should be useful for evaluating the significance and consequences of such behaviors for individuals, organizations, [44][45][46][47][48][49][50][51][52] and society in the future. [53][54][55][56][57] Specifically, we wanted to know how common presenteeism is among students belonging to the generation of Millennials and whether they favor presenteeism over absenteeism when they are sick. We were particularly interested in the question of whether they differ in their behavior with regard to study and work times and whether their behavior is associated with other health-related variables. To investigate this, we conducted an online survey.
When studying presenteeism, two methodological issues need to be borne in mind: Previous studies have usually not differentiated between individuals suffering from health events-who are thus able to show SP-and individuals without health problems-who per definition cannot show SP behavior. 58 Therefore, these studies have provided information about the prevalence of SP in the workforce but not about the prevalence among sick employees. In addition, it is necessary to distinguish between SP rates and SP propensity. 59 SP rates are measures of the frequency of attending work while ill. They depend on the number of health events and are an indicator of health status or vulnerability to illness. 60 SP propensity is the percentage of days worked while ill over the total number of days that the person was sick, 32 and it reflects an individual's probability of opting for sickness presence rather than sickness absence in the case of illness. 60 Thus, it offers additional information with regard to the decision-making process of the individual. Both aspects were considered in the current study.

Study design and population
Based on Krejcie and Morgan's (1970) 61 specifications for the calculation of a representative sample, we calculated a required sample size of 384 by taking into account a confidence interval of two standard deviations, the degree of accuracy of 0.05, and a total population of 2.9 million students in Germany. 62 During the 2018 summer term, we asked 15 random German institutions of higher education if they would allow us to send our survey to their students. Of these, four institutions agreed to forward the survey. In the email that we sent to the students, we asked participants to forward the survey to other potentially interested persons. In total, students from nine German institutions of higher education took part in the online survey. Participants were informed that the survey was anonymous and voluntary and that they could withdraw their participation at any time.
Of the 1,291 individuals who began taking the online survey, 791 provided complete data.

Measures of presenteeism and absenteeism
Because many students do not only study full time but are also employed in paid part-time jobs to contribute to their living, we collected data on presenteeism and absenteeism separately for school and work. To measure SP frequency, students were asked how often during the past twelve months they went to classes when the state of their health would have justified staying home. 1 9 63 The same question was posed for going to work. Whereas fixed response categories such as "never," "once," "2 to 5 times," and "more than 5 times" have been used in other studies, 1 30 63 64 we used an openquestion format. The reason for this was that the former is seen as too crude for such a low base rate behavior and might convey information about what is perceived as normal and might thus bias the answers. 65 Sickness absence (SA) was also measured with two items asking students to indicate how often during the past twelve months they stayed home due to sickness instead of going to classes/work.

Health-and personality-related factors
As potential correlates of SP, we collected subjective measures of individual health, locus of control, professional self-efficacy, and extent of paid work. Because in Germany health-related issues and objective health status are very sensitive topics, we decided to use a subjective measure of individual health, which is known to be a robust predictor of several health outcomes, such as functional ability, health care utilization, and morbidity. 66 Locus of control is "a fundamental individual difference variable that reflects individuals' beliefs about the degree of control they have over events in their lives" (Galvin et al., 2018, p. 820). 67 People with an internal locus of control are convinced that their fate depends on their decisions, efforts, and behaviors. Individuals with an external locus of control believe that their lives are controlled by external forces such as powerful others, chance, or luck. The construct is often applied in the area of health psychology. [68][69][70][71][72][73] Self-efficacy is one's belief in one's competence to perform intended actions. Efficacy beliefs influence the self-regulation of motivation through goal challenges and outcome expectations and the types of activities people choose. 74 Selfefficacy and locus of control (especially health locus of control) are seen as personal health resources that determine health-related behavior. 73 Both concepts have repeatedly been used in studies of the health-related behaviors of students. 73 75-78 In addition, we thought the extent of paid work would be a relevant correlate because it is an indicator of workload, which is known to be related to presenteeism. 3 With regard to students' health status, we used two variables based on a sequence of subjective assessments. We measured participants' proclivity to adopt a sick role 65 as the mean of their answers to nine items. Items asked them to rate how sick they would be if they were to suffer from certain health impairments (e.g., "Imagine you are suffering from a bad headache. How sick are you?") on a 7-point rating format (1="very sick"; 7="not at all sick"). Subjective health status was calculated as the mean of two items ("How do you rate your general susceptibility to disease?"; "How do you rate your health in comparison with your age group?"). The scale was a slider ranging from 0 ("very low"; "very bad") to 100 ("very high"; "very good"). We used the 4-item short scale by Kovaleva et al.  79 to measure locus of control ("When I really try, I will succeed") and three items from the short scale of occupational self-efficacy 80 (e.g., "I am not sure I have all the abilities necessary for my job"). Both locus of control and occupational self-efficacy are stable characteristics that are relevant to presenteeism. 65 81 82 Response categories for the seven items ranged from 1 ("does not apply at all") to 5 ("fully applies").

Employment and demographic variables
Participants stated whether they had worked before they started their university program, and they were asked if and how many hours they worked while attending school and during semester breaks.
The survey asked for demographic information on gender, age, study major, pursued degree, and name of university. Employment and demographic variables were measured with one item each.

Data analyses
The number of health events was calculated as the sum of the SP and SA frequencies. We computed presenteeism propensity as SP frequency divided by the number of health events for university and work settings separately. Hence, SA propensity was 1-SP propensity. 60  of the questions did not apply to all participants (e.g., those referring to working while studying), and analyses of subgroups differed in sample sizes. Participants who had missing data on one of the investigated variables were excluded from the respective analysis.

Ethics approval and informed consent of participants
The study was approved by the ethics commission of the German Society for Psychology (DGPs).
Before beginning the study, participants were informed that their participation was voluntary and that they could withdraw their participation at any time while working on the questionnaire. They were informed that no personalized data would be collected, that their data would be used for scientific purposes only, and that it would be stored and analyzed anonymously so that it would not be possible to establish any connection between them and their answers.

Patient and public involvement
Neither subjects nor public were involved in the study.

Results
A total of 791 questionnaires were completed. In accordance with the goal of the study, the analyses were restricted to participants belonging to the generation of interest, the Millennials, which include people who were born in 1981 or later. 36 41 Further, cases of long-term absence or presence were excluded from the analyses because these were likely to have been caused by different modalities. 60 As was done in other studies, we defined 60 days as the threshold. 60  Social Work / Education 79 49 Legal Studies 15 10 Design 8 2 Journalism 17 12 Mathematics / Chemistry 23 18 Communication 41 17 Media 51 27 Other Study Programs 37 18 Not specified 578 104 Sickness. The descriptive results for the number of days of sickness in the past twelve months and the correlations with other factors can be found in   Table 3 (left side). For the further exploration of SP behavior and its correlates, the analyses were restricted to participants who reported at least one incident of sickness. The reason for this is that only individuals who reported some kind of illness during the past twelve months were able to show presenteeism (see Table 3, right side). As results show, 72.8% of the sample were left for analyses regarding SP at school (N=545) and 69.7% with regard to work (N=468). Therefore, after excluding "healthy" participants, the SP rates rose to 87.9% during school time and 87% during work time.  Table 4. between SP frequency and presenteeism propensity; however, because the formula for presenteeism propensity contains SP frequency, it would not be productive to report them.
The probability of going to classes when sick was significantly higher than the probability of staying home (Z(544)=-10.042, p<0.001). With regard to work time, the pattern was quite similar: The probability of going to work while ill was significantly higher than the probability of staying home

Discussion
In this survey, SP rates for the complete sample were 64% at school and 60.4% at work with more than one fourth of the participants stating that they had not been sick during the past year. While recent research among German employees has reported great variability in rates ranging from 35% 85 to more than 90%, 86 the levels found here were in the same range as studies that were conducted with employees in the Netherlands, 28 Scandinavia, 86 and other European countries. 23 The proportion of participants who reported no health event during the past year was higher than in other studies. 60 This higher rate might be due to the fact that the sample we investigated was younger than the usual workforce samples and the fact that age was positively related to health issues. [87][88][89] In our analyses, we followed Navarro et al.'s (2018) 58 recommendation to separately identify the SP prevalence for the subsample of individuals who reported some kind of illness and were thus able to show SP.
Hence, the rates increased by more than 35-40%. This increase was lower than in the study by , 58 who reported SP rates of 23% for the complete sample and a rate that was more than doubled for those with health problems (53%). However, in our survey, SP levels were much higher. The distinction between SP rates for the complete sample and the subsample of those who experienced health problems provides answers to two separate questions. The first (the whole sample) indicates the economic significance of the problem, whereas the second (the subsample) can provide HRM and corporate health management with relevant information as to how many employees need support and what kinds of measures might be helpful. 89 90 Therefore, both methods of calculation are useful; however, in terms of health interventions, it is more appropriate to consider the part of the workforce reporting some kind of illness. 58 89 90  The presenteeism propensities for school and work were identical, which means that participants' decision making did not differ between the two settings. Propensities showed that on average, in 2 out of 3 cases, participants who were sick chose to attend class or go to work and thus showed significantly more SP than SA. To date, only a few studies have explored presenteeism propensities. 32 60 A Canadian study reported a propensity of .50 for employees, 32 and an Austrian study reported a propensity of .59, also for employees. 60 The propensities found in the current study for students appeared to be slightly higher (.67 and .68). This finding seems to contradict the focus on work-life balance that has been reported for this generation of Millennials. 41 43 91 92 The high levels of presenteeism propensity might be explained by students who might be worried that they will not to be able to keep up if they miss too many classes. 93 With regard to their jobs, the high level might be due to their work conditions, that is, most of them are probably paid on an hourly basis with the consequence that they will not earn anything if they call in sick. A more detailed view of the data revealed that the proportion of participants who always decided for SP when they were sick was more than three times higher than those who always chose SA. Millennials' attributes and expectations offer further potential explanations for their high attendance rates. 94 Millennials favor close relationships at work 95 and prefer team work inter alia in order to avoid risks. 93 Furthermore, they are interested in the acquisition of skills. 96 Thus, their decision to embrace presenteeism might reflect their desire not to let down team members (either at school or at work) and to expand their competencies. 86 Future studies should investigate whether this high propensity is due to differences in "jobs" (i.e., studying full time and working part time versus working full time) or due to different generations. We suggest that a survey be administered to full-time employees who belong to the generation of Millennials.
Although those who reported at least some kind of illness reported a larger number of days of sickness during school time than during work time, SP at school and SP at work were strongly correlated. That indicates that both kinds of behavior are determined by individuals' health status, which is reflected in the number of days they were sick and the positive correlation with their  3 found that individuals with poorer general health exhibited more presenteeism because the sheer number of health events was higher, a finding that was supported by the data in the current study. In addition, the positive correlation between SP and SA also found here has been well established, 1 6 17 21 63 65 although it seemed particularly high in this study.
In our study, SP was positively associated with good subjective health and an external locus of control and negatively correlated with occupational self-efficacy. The correlation between SP and subjective health status has been well established. 65 However, there is only one earlier study we know of that investigated the relation between health locus of control and presenteeism among employees in all age groups, and it found lower SP for people with an internal health locus of control. 97 Although we measured general locus of control, we found the same pattern: that is, a higher SP rate for individuals with an external locus of control. Research has shown that university students score higher on internal locus of control than on external locus of control 78 and that an internal locus of control and a high level of self-efficacy 98 are associated with academic achievement. 75 Thus, students with an external locus of control might worry that they will miss too much if they do not attend classes when they are ill. Self-efficacy has been postulated to be associated with SP. 2 81 A study involving a sample of Chinese full-time workers established a positive correlation between SP and self-efficacy and found that self-efficacy could buffer the negative effect of SP on health. 82 By contrast, in our study, participants with low occupational self-efficacy showed higher levels of SP. The difference in findings may have occurred because Lu et al. (2014) 82 measured general self-efficacy, whereas we used occupational self-efficacy. In addition, research has shown that Millennials are high in self-efficacy, 92 94 and thus, they might be convinced that they can manage to make up any work they miss when they miss school or work when they are sick. By contrast, participants with low occupational self-efficacy are not sure whether they have the necessary competencies to meet expectations and thus opt for SP in order to work as much as possible and

Strengths and weaknesses
Pertaining to the goal of the study to investigate SP among the generation of Millennials, a strength of the survey is that it provided information about the SP behavior of the future workforce, a group that has rarely been investigated with regard to SP. In addition, to our knowledge, the study is one of the first to explore SP among students who belong to the generation of Millennials. Further, since many of the participants were not just studying but were also working part time, this study allowed us to assess SP behavior in university and work settings at the same time and to compare them.
However, it is obvious that the sample was restricted to students and thus does not allow generalizations about manifestations of SP behavior among full-time employees in these birth cohorts. Additional advantages of the study are that we calculated propensities and made a distinction between individuals with and without health problems. In most studies to date, participants have been asked to quantify the number of times they have engaged in SP but not the number of times they have engaged in SA or the total number of health events they have experienced. Thus, the prevalence of SP could be reported only for the complete sample.
Shortcomings of the survey pertain mostly to methodological issues: Because we applied a crosssectional design, we were not able to identify the direction of the influence between subjective health and SP. Another weakness is that all measures were self-reports, and thus, their reliability might suffer from common method bias and overreporting due to social desirability. 65 Due to missing data and the non-applicability of questions, some of the analyses were restricted to a much smaller number of participants than the total sample size. In addition, as in many other studies, 3 participants were asked to recall incidents of sickness presence and absence over a one-year period, and therefore, the data might be biased by false recollection. 99 However, because the self-reported measure of days of sickness 99

Conclusion
The study's results are in accordance with recent findings that the prevalence of SP is continuously rising, 101 which means the issue will remain an important one. SP and the associated risks are not restricted to the current workforce but are prevalent among those who are currently enrolled in a university. One should think about implementing health education concerning SP for students who represent the future workforce and soon-to-be managers in order to sensitize them to the management of SP before they join the full-time workforce. A future study should be conducted in order to compare the results of this survey of Millennials attending a university with full-time working Millennials. Further, presenteeism propensity is important for gaining insights into individuals' decisions to engage in presenteeism or absenteeism when ill. With regard to methodology, future studies should make a distinction in prevalence rates between the complete workforce and those with health problems because these two rates provide answers to different questions.

Author Contributions
DL and FR contributed to the conception and design of the study as well as to the collection and assembly of the data. DL and FR contributed to the statistical analysis, the interpretation of the data, and the drafting of the manuscript.

Funding
This research received no specific grant from any funding agency in the public, commercial, or notfor-profit sectors.

Conflicting interests
None declared.

Ethics approval
The study was approved by the ethics commission of the German Society for Psychology (DGPs).

Informed consent
Participants gave informed consent before taking part in the survey and could withdraw their participation at any time.

Data sharing statement
Data are available. Please contact corresponding author.

Instructions to authors
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Millennials: Sickness presenteeism and its correlates -A cross-sectional online survey
Abstract Objective: Sickness presenteeism (SP) is a well-documented phenomenon in the current workforce.
However, little is known about the SP of future employees (Millennials). We investigated the rate and propensity of presenteeism as well as health-and work-related correlates in university students to obtain information about the relevance of SP in the future work force.
Design and setting: We administered a cross-sectional online survey in August 2018 involving selfassessments of health-and work-related behavior. As planned, we analyzed rates, instances, and propensities of presenteeism and absenteeism. The target population was Millennial university students. Subjective health explained 9.2% of the variance in SP at school (β=0.279) and 9.9% of the variance in SP at work (β=0.272).

Conclusions:
The SP rates of the future work force were in line with previous research on older employees, whereas the presenteeism propensities we found here were higher. Across all analyses, subjective health proved to be associated with presenteeism. Thus, the relevance of SP will remain constant or might even increase with regard to the future workforce. Programs offering health education should be implemented in order to sensitize this generation as early as possible.

Introduction
Sickness presenteeism (SP) refers to going to work while ill. 1 The study of SP has gained in importance during the past two decades due to its association with sickness absenteeism, productivity, health, and attitudes. 2  productivity loss 13 and a decline in work attitudes. 14 15 Considering consequences for the employing organization, there is empirical evidence for uncovered costs caused by productivity loss. 16 SP has been reported independently of a variety of sociodemographic variables 1 17-23 and for various kinds of professional groups. 17 19 24-29 SP is a global phenomenon. Its prevalence has been documented in many countries in Europe, 17 25 29 30 the U.S., 31 Canada, 32 33 Asia, 34 and the Middle East. 35 The presenteeism rates reported for study samples vary from 30% to more than 90%.
Due to the wide range of negative effects of SP for individuals and organizations as well as the global ubiquity of SP, the study of SP seems advisable. However, although SP rates are well documented for the current workforce, the majority of which belong to the generations of Baby Boomers and Generation X, 36 37 empirical evidence concerning the SP behavior of the future generation of workers is scarce. [38][39][40] Matsushita and colleagues (2011) 39 developed an instrument to measure presenteeism among students, but they did not report on presenteeism behavior. Johansen (2018) 38 analyzed motives for the presenteeism of students in secondary school. To our knowledge, the study by Kötter, Obst, and Voltmer (2017) 40 is the only one to date to investigate the presenteeism behavior of students. They did not find any differences in prevalence rates between medical students and STEM students and reported higher levels of presenteeism for female than for male students.
However, the prevalence rate they reported could not be compared with other studies because their way of measuring and aggregating presenteeism behavior was uncommon. Current university students are predominantly classified as Millennials, 36 41 who are said to have different attitudes  42 and they hold a "work-to-live" attitude with a higher priority on work-life balance 41 43 than previous generations. Especially this latter trend suggests that presenteeism among Millennials should be lower than among older generations. In general, interests and work values are relatively stable 37 and are associated with behavior. Thus, knowledge about the SP-related behaviors of current students should be useful for evaluating the significance and consequences of such behaviors for individuals, organizations, [44][45][46][47][48][49][50][51][52] and society in the future. [53][54][55][56][57] Specifically, we wanted to know how common presenteeism is among students belonging to the generation of Millennials and whether they favor presenteeism over absenteeism when they are sick. We were particularly interested in the question of whether they differ in their behavior with regard to study and work times and whether their behavior is associated with other health-related variables. To investigate this, we conducted an online survey.
When studying presenteeism, two methodological issues need to be borne in mind: Previous studies have usually not differentiated between individuals suffering from health events-who are thus able to show SP-and individuals without health problems-who per definition cannot show SP behavior. 58 Therefore, these studies have provided information about the prevalence of SP in the workforce but not about the prevalence among sick employees. In addition, it is necessary to distinguish between SP rates and SP propensity. 59 SP rates are measures of the frequency of attending work while ill. They depend on the number of health events and are an indicator of health status or vulnerability to illness. 60 SP propensity is the percentage of days worked while ill over the total number of days that the person was sick, 32 and it reflects an individual's probability of opting for sickness presence rather than sickness absence in the case of illness. 60 Thus, it offers additional information with regard to the decision-making process of the individual. Both aspects were considered in the current study.

Study design and population
Based on Krejcie and Morgan's (1970) 61 specifications for the calculation of a representative sample, we calculated a required sample size of 384 by taking into account a confidence interval of two standard deviations, the degree of accuracy of 0.05, and a total population of 2.9 million students in Germany. 62 During the 2018 summer term, we asked 15 random German institutions of higher education if they would allow us to send our survey to their students. Of these, four institutions agreed to forward the survey. In the email that we sent to the students, we asked participants to forward the survey to other potentially interested persons, which led to a further distribution of the survey and thus in total, students from nine German institutions of higher education took part in the online survey. Participants were informed that the survey was anonymous and voluntary and that they could withdraw their participation at any time. Of the 1,291 individuals who began taking the online survey, 791 provided complete data.

Measures of presenteeism and absenteeism
Because many students do not only study full time but are also employed in paid part-time jobs to contribute to their living, we collected data on presenteeism and absenteeism separately for school and work. To measure SP frequency, students were asked how often during the past twelve months they went to classes when the state of their health would have justified staying home. 1 9 63 The same question was posed for going to work. Whereas fixed response categories such as "never," "once," "2 to 5 times," and "more than 5 times" have been used in other studies, 1 30 63 64 we used an openquestion format. The reason for this was that the former is seen as too crude for such a low base rate behavior and might convey information about what is perceived as normal and might thus bias the answers. 65 Sickness absence (SA) was also measured with two items asking students to indicate how often during the past twelve months they stayed home due to sickness instead of going to classes/work. construct is often applied in the area of health psychology. [68][69][70][71][72][73] Self-efficacy is one's belief in one's competence to perform intended actions. Efficacy beliefs influence the self-regulation of motivation through goal challenges and outcome expectations and the types of activities people choose. 74 Selfefficacy and locus of control (especially health locus of control) are seen as personal health resources that determine health-related behavior. 73 Both concepts have repeatedly been used in studies of the health-related behaviors of students. 73 75-78 In addition, we thought the extent of paid work would be a relevant correlate because it is an indicator of workload, which is known to be related to presenteeism. 3 With regard to students' health status, we used two variables based on a sequence of subjective assessments. Subjective health status was calculated as the mean of two items ("How do you rate your general susceptibility to disease?"; "How do you rate your health in comparison with your age group?"). The scale was a slider ranging from 0 ("very low"; "very bad") to 100 ("very high"; "very good"). We used the 4-item short scale by   79 to measure locus of control (e.g., "When I really try, I will succeed") and three items from the short scale of occupational self-efficacy 80 (e.g., "I am not sure I have all the abilities necessary for my job"). Both locus of control and  65 81 82 Response categories for the seven items ranged from 1 ("does not apply at all") to 5 ("fully applies").

Employment and demographic variables
Participants stated whether they had worked before they started their university program, and they were asked if and how many hours they worked while attending school and during semester breaks.
The survey asked for demographic information on gender, age, study major, pursued degree, and name of university. Employment and demographic variables were measured with one item each.

Data analyses
The number of health events was calculated as the sum of the SP and SA frequencies. 33 60 We computed presenteeism propensity as SP frequency divided by the number of health events for university and work settings separately. Hence, SA propensity was 1-SP propensity. 60  However, it was not compulsory to provide an answer to each question because some of the questions did not apply to all participants (e.g., those referring to working while studying). Thus, analyses of subgroups differed in sample sizes. Participants who had missing data on one of the investigated variables were excluded from the respective analysis.

Ethics approval and informed consent of participants
The study was approved by the ethics commission of the German Society for Psychology (DGPs).
Before beginning the study, participants were informed that their participation was voluntary and that they could withdraw their participation at any time while working on the questionnaire. They were informed that no personalized data would be collected, that their data would be used for scientific purposes only, and that it would be stored and analyzed anonymously so that it would not be possible to establish any connection between them and their answers.

Patient and public involvement
Neither subjects nor public were involved in the study.

Results
A total of 791 questionnaires were completed. In accordance with the goal of the study, the analyses were restricted to participants belonging to the generation of interest, the Millennials, which include people who were born in 1981 or later. 36 41 Further, cases of long-term absence or presence were excluded from the analyses because these were likely to have been caused by different modalities. 60 As was done in other studies, we defined 60 days as the threshold. 60  Not specified 578 32.6 104 13.9 * Participants included in the analyses were those who completed the questionnaire and belonged to the generation of Millennials Sickness. The descriptive results for the number of days of sickness in the past twelve months can be found in Table 2 and the correlations with other factors in Table 3. It turned out that participants who worked while attending school reported a significantly larger number of days of sickness during school time than during work time. Further, the correlation between days of sickness during school  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59    Correlates of SP: With regard to SP at school, we found a significant correlation with SP at work (Rho=0.49, p=0.000). Further correlations for SP during school and work time are listed in Table 5. In order to further investigate the two most important correlates, we computed multiple linear regressions using ordinary least square method and variables selection method "Enter" (consideration of both variables). Linearity, multicollinearity and homoscedasticity. First, we checked for whether the assumptions for the application of the method were fulfilled. 84 Data were collected through independent random sampling. Inspection of scatterplots of the independent variables against the dependent and unstandardized predicted values against studentized residuals indicated that the assumption of linearity between independent and dependent variables was met. In addition, the assumptions with respect to homoscedascity and multicollinearity were met. Outliers were identified in two ways. First, all subjects with values above or below three standard deviations of studentized deleted residuals were eliminated from the analyses. Second, on the basis of the leverage index, all subjects with values above the critical value (i.e., 2*p/n) 85 were excluded from the analyses. Thus, 410 subjects were left for the analysis of presenteeism at school and 314 subjects for the analysis of presenteeism at work (Table 6). between SP frequency and presenteeism propensity; however, because the formula for presenteeism propensity contains SP frequency, it would not be productive to report them.
The probability of going to classes when sick was significantly higher than the probability of staying home (Z(544)=-10.042, p=0.000). With regard to work time, the pattern was quite similar: The probability of going to work while ill was significantly higher than the probability of staying home (Z(467)=-9.444, p=0.000). There were no gender differences in presenteeism propensity during school or work time.

Discussion
Aim of the survey was to obtain information about the presenteeism behavior of studying Millennials who constitute the future workforce. While more than one fourth of participants reported no incidents of sickness during the past year, those who reported at least some kind of illness reported a In this survey, SP rates for the complete sample were on an average level in comparison to recent research among German employees that has reported great variability in rates ranging from 35% 86 to more than 90%. 87 The levels found here were in the same range as studies that were conducted with employees in the Netherlands, 28 Scandinavia, 87 and other European countries. 23 The proportion of participants who reported no health event during the past year was higher than in other studies. 60 This higher rate might be due to the fact that the sample we investigated was younger than the usual workforce samples and the fact that age was positively related to health issues. [88][89][90] In our analyses, we followed Navarro et al.'s (2018) 58 recommendation to separately identify the SP prevalence for the subsample of individuals who reported some kind of illness and were thus able to show SP.
Hence, the rates increased by more than 35-40%. This increase was lower than in the study by , 58 who reported SP rates of 23% for the complete sample and a rate that was more than doubled for those with health problems (53%). However, in our survey, SP levels were much higher. The distinction between SP rates for the complete sample and the subsample of those who experienced health problems provides answers to two separate questions. The first (the whole sample) indicates the economic significance of the problem, whereas the second (the subsample) can provide HRM and corporate health management with relevant information as to how many employees need support and what kinds of measures might be helpful. 90 91 Therefore, both methods of calculation are useful; however, in terms of health interventions, it is more appropriate to consider the part of the workforce reporting some kind of illness. 58 90 91 The presenteeism propensities for school and work were identical, which means that participants' decision making did not differ between the two settings. Propensities showed that on average, in 2  32 and an Austrian study reported a propensity of .59, also for employees. 60 The propensities found in the current study for students appeared to be slightly higher (.67 and .68). This finding seems to contradict the focus on work-life balance that has been reported for the generation of Millennials. 41 43 92 93 The high levels of presenteeism propensity might be explained by students who might be worried that they will not be able to keep up if they miss too many classes. 94 With regard to their jobs, the high level might be due to their work conditions, that is, most of them are probably paid on an hourly basis with the consequence that they will not earn anything if they call in sick. A more detailed view of the data revealed that the proportion of participants who always decided for SP when they were sick was more than three times higher than those who always chose SA. Millennials' attributes and expectations offer further potential explanations for their high attendance rates. 95 Millennials favor close relationships at work 96 and prefer team work inter alia in order to avoid risks. 94 Furthermore, they are interested in the acquisition of skills. 97 Thus, their decision to embrace presenteeism might reflect their desire not to let down team members (either at school or at work) and to expand their competencies. 87 Future studies should investigate whether this high propensity is due to differences in "jobs" (i.e., studying full time and working part time versus working full time) or due to different generations. We suggest that a survey be administered to full-time employees who belong to the generation of Millennials.
The high correlation between SP at school and SP indicates that both kinds of behavior are determined by individuals' health status, which is reflected in the number of days they were sick and the positive correlation with their subjective assessment of their health. Miraglia and Johns (2016) 3 found that individuals with poorer general health exhibited more presenteeism because the sheer number of health events was higher, a finding that was supported by the data in the current study. In addition, the positive correlation between SP and SA also found here has been well established, 1 6 17 21 63 65 although it seemed particularly high in this study.
In our correlational analyses, SP was positively associated with good subjective health and an external locus of control and negatively correlated with occupational self-efficacy. The correlation between SP and subjective health status has been well established. 65 In addition, the multiple linear regressions with the two most important correlates (i.e., subjective health and locus of control) revealed that subjective health is a significant predictor for SP in both contexts. This means the better participants perceive their health the more SP they report. This has to be taken into consideration in future measures to manage SP. There is only one earlier study we know of that investigated the relation between health locus of control and presenteeism among employees in all age groups, and it found lower SP for people with an internal health locus of control. 98 Although we measured general locus of control, we found the same pattern: that is, a higher SP rate for individuals with an external locus of control. Research has shown that university students score higher on internal locus of control than on external locus of control 78 and that an internal locus of control and a high level of self-efficacy 99 are associated with academic achievement. 75 Thus, students with an external locus of control might worry that they will miss too much if they do not attend classes when they are ill. Self-efficacy has been postulated to be associated with SP. 2  whereas we used occupational self-efficacy. In addition, research has shown that Millennials are high in self-efficacy, 93 95 and thus, they might be convinced that they can manage to make up any work they miss when they miss school or work when they are sick. By contrast, participants with low occupational self-efficacy are not sure whether they have the necessary competencies to meet

Strengths and weaknesses
Pertaining to the goal of the study to investigate SP among the generation of Millennials, a strength of the survey is that it provided information about the SP behavior of the future workforce, a group that has rarely been investigated with regard to SP. In addition, to our knowledge, the study is one of the first to explore SP among students who belong to the generation of Millennials. Further, since many of the participants were not just studying but were also working part time, this study allowed us to assess SP behavior in university and work settings at the same time and to compare them.
However, it is obvious that the sample was restricted to students and thus does not allow generalizations about manifestations of SP behavior among full-time employees in these birth cohorts. Additional advantages of the study are that we calculated propensities and made a distinction between individuals with and without health problems. In most studies to date, participants have been asked to quantify the number of times they have engaged in SP but not the number of times they have engaged in SA or the total number of health events they have experienced. Thus, the prevalence of SP could be reported only for the complete sample.
Shortcomings of the survey pertain mostly to methodological issues: Because we applied a crosssectional design, we were not able to identify the direction of the influence between subjective health and SP. Another weakness is that all measures were self-reports, and thus, their reliability might suffer from common method bias and overreporting due to social desirability. 65 Due to missing data and the non-applicability of questions, some of the analyses were restricted to a much smaller number of participants than the total sample size. In addition, as in many other studies, 3 participants were asked to recall incidents of sickness presence and absence over a one-year period, and therefore, the data might be biased by false recollection. 100 However, because the self-reported measure of days of sickness 100

Conclusion
The study's results are in accordance with recent findings that the prevalence of SP is continuously rising, 102 which means the issue will remain an important one. Further, they indicate that especially subjective health is associated with presenteeism behavior of Millennials. SP and the associated risks are not restricted to the current workforce but are prevalent among those who are currently enrolled in a university. One should think about implementing health education concerning SP for students who represent the future workforce and soon-to-be managers in order to sensitize them to the management of SP before they join the full-time workforce. A future study should be conducted in order to compare the results of this survey of Millennials attending a university with full-time working Millennials. Further, presenteeism propensity is important for gaining insights into individuals' decisions to engage in presenteeism or absenteeism when ill. With regard to methodology, future studies should make a distinction in prevalence rates between the complete workforce and those with health problems because these two rates provide answers to different questions.

Author Contributions
DL and FR contributed to the conception and design of the study as well as to the collection and assembly of the data. DL and FR contributed to the statistical analysis, the interpretation of the data, and the drafting of the manuscript.

Funding
This research received no specific grant from any funding agency in the public, commercial, or notfor-profit sectors.

Conflicting interests
None declared.

Ethics approval
The study was approved by the ethics commission of the German Society for Psychology (DGPs).

Informed consent
Participants gave informed consent before taking part in the survey and could withdraw their participation at any time.

Data sharing statement
Data are available. Please contact corresponding author.

Instructions to authors
Complete this checklist by entering the page numbers from your manuscript where readers will find each of the items listed below.
Your article may not currently address all the items on the checklist. Please modify your text to include the missing information. If you are certain that an item does not apply, please write "n/a" and provide a short explanation.
Upload your completed checklist as an extra file when you submit to a journal.
In your methods section, say that you used the STROBE cross sectional reporting guidelines, and cite them as:

Millennials: Sickness presenteeism and its correlates -A cross-sectional online survey
Abstract Objective: Sickness presenteeism (SP) is a well-documented phenomenon in the current workforce.
However, little is known about the SP of future employees (Millennials). We investigated rate and propensity of presenteeism and health-and work-related correlates in university students to obtain information about the relevance of SP in the future work force.
Design and setting: We administered a cross-sectional online survey in August 2018 involving selfassessments of health-and work-related behavior. As planned, we analyzed rates, instances, and propensities of presenteeism and absenteeism. The target population was Millennial university students.

Conclusions:
The SP rates of the future work force were in line with previous research on older employees, whereas the presenteeism propensities we found here were higher. Across all analyses, subjective health proved to be associated with presenteeism. Thus, the relevance of SP will remain constant or might even increase with regard to the future workforce. Programs offering health education should be implemented to sensitize this generation as early as possible.

Introduction
Sickness presenteeism (SP) refers to going to work while ill. 1 The study of SP has gained in importance during the past two decades due to its association with sickness absenteeism, productivity, health, and attitudes. 2  productivity loss 13 and a decline in work attitudes. 14 15 Considering consequences for the employing organization, there is empirical evidence for uncovered costs caused by productivity loss. 16 SP has been reported independently of a variety of sociodemographic variables 1 17-23 and for various kinds of professional groups. 17 19 24-29 SP is a global phenomenon. Its prevalence has been documented in many countries in Europe, 17 25 29 30 the U.S., 31 Canada, 32 33 Asia, 34 and the Middle East. 35 The presenteeism rates reported for study samples vary from 30% to more than 90%.
Due to the wide range of negative effects of SP for individuals and organizations as well as the global ubiquity of SP, the study of SP seems advisable. However, although SP rates are well documented for the current workforce, the majority of which belong to the generations of Baby Boomers and Generation X, 36 37 empirical evidence concerning the SP behavior of the future generation of workers is scarce. [38][39][40] Matsushita and colleagues (2011) 39 developed an instrument to measure presenteeism among students, but they did not report on presenteeism behavior. Johansen (2018) 38 analyzed motives for the presenteeism of students in secondary school. To our knowledge, the study by   40 is the only one to date to investigate the presenteeism behavior of students. They did not find any differences in prevalence rates between medical students and STEM students and reported higher levels of presenteeism for female than for male students.
However, the prevalence rate they reported could not be compared with other studies because their way of measuring and aggregating presenteeism behavior was uncommon. Current university students are predominantly classified as Millennials, 36 41 who are said to have different attitudes  42 and they hold a "work-to-live" attitude with a higher priority on work-life balance 41 43 than previous generations. Especially this latter trend suggests that presenteeism among Millennials should be lower than among older generations. In general, interests and work values are relatively stable 37 and are associated with behavior. Thus, knowledge about the SP-related behaviors of current students should be useful for evaluating the significance and consequences of such behaviors for individuals, organizations, [44][45][46][47][48][49][50][51][52] and society in the future. [53][54][55][56][57] Specifically, we wanted to know how common presenteeism is among students belonging to the generation of Millennials and whether they favor presenteeism over absenteeism when they are sick. We were particularly interested in the question of whether they differ in their behavior with regard to study and work times and whether their behavior is associated with other health-related variables. To investigate this, we conducted an online survey.
When studying presenteeism, two methodological issues need to be borne in mind: Previous studies have usually not differentiated between individuals suffering from health events-who are thus able to show SP-and individuals without health problems-who per definition cannot show SP behavior. 58 Therefore, these studies have provided information about the prevalence of SP in the workforce but not about the prevalence among sick employees. In addition, it is necessary to distinguish between SP rates and SP propensity. 59 SP rates are measures of the frequency of attending work while ill. They depend on the number of health events and are an indicator of health status or vulnerability to illness. 60 SP propensity is the percentage of days worked while ill over the total number of days that the person was sick, 32 and it reflects an individual's probability of opting for sickness presence rather than sickness absence in the case of illness. 60 Thus, it offers additional information with regard to the decision-making process of the individual. Both aspects were considered in the current study.

Study design and population
Based on Krejcie and Morgan's (1970) 61 specifications for the calculation of a representative sample, we calculated a required sample size of 384 by taking into account a confidence interval of two standard deviations, the degree of accuracy of 0.05, and a total population of 2.9 million students in Germany. 62 During the 2018 summer term, we asked 15 random German institutions of higher education if they would allow us to send our survey to their students. Of these, four institutions agreed to forward the survey. In the email that we sent to the students, we asked participants to forward the survey to other potentially interested persons, which led to a further distribution of the survey and thus in total, students from nine German institutions of higher education took part in the online survey. Participants were informed that the survey was anonymous and voluntary and that they could withdraw their participation at any time. Of the 1,291 individuals who began taking the online survey, 791 provided complete data.

Measures of presenteeism and absenteeism
Because many students do not only study full time but are also employed in paid part-time jobs to contribute to their living, we collected data on presenteeism and absenteeism separately for school and work. To measure SP frequency, students were asked how often during the past twelve months they went to classes when the state of their health would have justified staying home. 1 9 63 The same question was posed for going to work. Whereas fixed response categories such as "never," "once," "2 to 5 times," and "more than 5 times" have been used in other studies, 1 30 63 64 we used an openquestion format. The reason for this was that the former is seen as too crude for such a low base rate behavior and might convey information about what is perceived as normal and might thus bias the answers. 65 Sickness absence (SA) was also measured with two items asking students to indicate how often during the past twelve months they stayed home due to sickness instead of going to classes/work.

Health-and personality-related factors
As potential correlates of SP, we collected subjective measures of individual health, locus of control, professional self-efficacy, and extent of paid work. Because in Germany health-related issues and objective health status are very sensitive topics, we decided to use a subjective measure of individual health, which is known to be a robust predictor of several health outcomes, such as functional ability, health care utilization, and morbidity. 66 Locus of control is "a fundamental individual difference variable that reflects individuals' beliefs about the degree of control they have over events in their lives" (Galvin et al., 2018, p. 820). 67 People with an internal locus of control are convinced that their fate depends on their decisions, efforts, and behaviors. Individuals with an external locus of control believe that their lives are controlled by external forces such as powerful others, chance, or luck. The construct is often applied in the area of health psychology. [68][69][70][71][72][73] Self-efficacy is one's belief in one's competence to perform intended actions. Efficacy beliefs influence the self-regulation of motivation through goal challenges and outcome expectations and the types of activities people choose. 74 Selfefficacy and locus of control (especially health locus of control) are seen as personal health resources that determine health-related behavior. 73 Both concepts have repeatedly been used in studies of the health-related behaviors of students. 73 75-78 In addition, we thought the extent of paid work would be a relevant correlate because it is an indicator of workload, which is known to be related to presenteeism. 3 With regard to students' health status, we used two variables based on a sequence of subjective assessments. Subjective health status was calculated as the mean of two items ("How do you rate your general susceptibility to disease?"; "How do you rate your health in comparison with your age group?"). The scale was a slider ranging from 0 ("very low"; "very bad") to 100 ("very high"; "very good"). We used the 4-item short scale by   79 to measure locus of control (e.g., "When I really try, I will succeed") and three items from the short scale of occupational self-efficacy 80 (e.g., "I am not sure I have all the abilities necessary for my job"). Both locus of control and  65 81 82 Response categories for the seven items ranged from 1 ("does not apply at all") to 5 ("fully applies").

Employment and demographic variables
Participants stated whether they had worked before they started their university program, and they were asked if and how many hours they worked while attending school and during semester breaks.
The survey asked for demographic information on gender, age, study major, pursued degree, and name of university. Employment and demographic variables were measured with one item each.

Data analyses
The number of health events was calculated as the sum of the SP and SA frequencies. 33 60 We computed presenteeism propensity as SP frequency divided by the number of health events for university and work settings separately. Hence, SA propensity was 1-SP propensity. 60  because some of the questions did not apply to all participants (e.g., those referring to working while studying). Thus, analyses of subgroups differed in sample sizes. Participants who had missing data on one of the investigated variables were excluded from the respective analysis.

Ethics approval and informed consent of participants
The study was approved by the ethics commission of the German Society for Psychology (DGPs).
Before beginning the study, participants were informed that their participation was voluntary and that they could withdraw their participation at any time while working on the questionnaire. They were informed that no personalized data would be collected, that their data would be used for scientific purposes only, and that it would be stored and analyzed anonymously so that it would not be possible to establish any connection between them and their answers.

Patient and public involvement
Neither subjects nor public were involved in the study.

Results
A total of 791 questionnaires were completed. In accordance with the goal of the study, the analyses were restricted to participants belonging to the generation of interest, the Millennials, which include people who were born in 1981 or later. 36 41 Further, cases of long-term absence or presence were excluded from the analyses because these were likely to have been caused by different modalities. 60 As was done in other studies, we defined 60 days as the threshold. 60 83 More than 99% of respondents reported fewer than 60 days of sickness absence or sickness presence. Thus, the final sample comprised 749 participants (49.5% women) between the ages of 19 and 37 years with an average age of 24.7 ± 3.6 years. Their mean academic progress was 4.5 ± 2.7 semesters. Less than 1% of participants had no work experience, and the mean number of hours spent working per week was 15.4 ± 10.3. For a summary of the demographic variables, see Table 1.  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  Not specified 578 32.6 104 13.9 * Participants included in the analyses were those who completed the questionnaire and belonged to the generation of Millennials Sickness. The descriptive results for the number of days of sickness in the past twelve months can be found in Table 2 and the correlations with other factors in Table 3. It turned out that participants who worked while attending school reported a significantly larger number of days of sickness during school time than during work time. Further, the correlation between days of sickness during school  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60   F  o  r  p  e  e  r  r  e  v  i  e  w  o  n  l  y   11 time and days of sickness during work time was significant (Rho=0.60, p=0.000). Furthermore, days of sickness during school time and during work time were both significantly correlated with subjective health, locus of control, occupational self-efficacy, and for work time, also with number of hours spent working per week. With regard to gender, women reported significantly more days of sickness during school time and during work time than men. 27.2% of the participants did not report any health event during the last twelve months during school time. Concerning work days, 30.3% reported no health events.   Table 4 (left side). For the further exploration of SP behavior and its correlates, the analyses were restricted to participants who reported at least one incident of sickness. The reason for this is that only individuals who reported some kind of illness  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60   F  o  r  p  e  e  r  r  e  v  i  e  w  o  n  l  y   12 during the past twelve months were able to show presenteeism (see Table 4, right side). As results show, 72.8% of the sample were left for analyses regarding SP at school (n=545) and 69.7% with regard to work (n=468). Therefore, after excluding "healthy" participants, the SP rates rose to 87.9% during school time and 87% during work time. The difference between SP incidents and SA incidents during school time was significant. When experiencing illness during school time, 39.6% always chose to go to classes, whereas 12.1% never did. With regard to work, the pattern was quite similar: SP incidents during work time differed significantly from SA incidents. 41.9% always chose to go to work in spite of illness, and 13% never did.

Correlates of SP:
With regard to SP at school, we found a significant correlation with SP at work (Rho=0.49, p=0.000). Further correlations for SP during school and work time are listed in Table 5.  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60   F  o  r  p  e  e  r  r  e  v  i  e  w  o  n  l  y   13 In order to further investigate the two most important correlates, we computed multiple linear regressions using ordinary least square method and variables selection method "Enter" (consideration of both variables). Linearity, multicollinearity and homoscedasticity. First, we checked for whether the assumptions for the application of the method were fulfilled. 84 Data were collected through independent random sampling. Inspection of scatterplots of the independent variables against the dependent and unstandardized predicted values against studentized residuals indicated that the assumption of linearity between independent and dependent variables was met. In addition, the assumptions with respect to homoscedascity and multicollinearity were met. Outliers were identified in two ways. First, all subjects with values above or below three standard deviations of studentized deleted residuals were eliminated from the analyses. Second, on the basis of the leverage index, all subjects with values above the critical value (i.e., 2*p/n) 85 were excluded from the analyses. Thus, 419 subjects were left for the analysis of presenteeism at school and 323 subjects for the analysis of presenteeism at work (Table 6).  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60   F  o  r  p  e  e  r  r  e  v  i  e  w  o  n  l  y   14 Analyses revealed significant models. Subjective health explained 9.7% of the variance of presenteeism frequencies for school time and 8.1% for work time, indicating that presenteeism frequencies were higher for participants with good subjective health in comparison with those with poor subjective health. In both models, the effect of locus of control was not significant.
Presenteeism propensity. Presenteeism propensity, which reflects an individual's probability of opting for presenteeism instead of absenteeism when suffering a health event, was 0.67 ± 0.34 at school and 0.68 ± 0.35 at work. Presenteeism propensity at school was significantly associated with presenteeism propensity at work (Rho=0.52, p=0.000). Of course, there were significant correlations between SP frequency and presenteeism propensity; however, because the formula for presenteeism propensity contains SP frequency, it would not be productive to report them.
The probability of going to classes when sick was significantly higher than the probability of staying home (Z(544)=-10.042, p=0.000). With regard to work time, the pattern was quite similar: The probability of going to work while ill was significantly higher than the probability of staying home (Z(467)=-9.444, p=0.000). There were no gender differences in presenteeism propensity during school or work time.

Discussion
Aim of the survey was to obtain information about the presenteeism behavior of studying Millennials who constitute the future workforce. While more than one fourth of participants reported no incidents of sickness during the past year, those who reported at least some kind of illness reported a larger number of days of sickness during school time than during work time. SP rates for the complete sample were 64.4% at school and 60% at work and for those participants reporting at least one health event 87.9% at school and 87% at work. Thus, the SP rates of the future work force were in line with previous research on older employees. Presenteeism propensities were 0.67 for school and 0.68 for work and were thus higher than reported in other studies. SP at school and SP at work  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60   F  o  r  p  e  e  r  r  e  v  i  e  w  o  n  l  y   15 were highly associated. Further, SP was positively correlated with good subjective health and an external locus of control and negatively correlated with occupational self-efficacy. Across all analyses, including multiple linear regressions, subjective health was the variable with the strongest association with SP. Results of the study show that the relevance of SP will remain constant or might even increase with regard to the future workforce.
In this survey, SP rates for the complete sample were on an average level in comparison to recent research among German employees that has reported great variability in rates ranging from 35% 86 to more than 90%. 87 The levels found here were in the same range as studies that were conducted with employees in the Netherlands, 28 Scandinavia, 87 and other European countries. 23 The proportion of participants who reported no health event during the past year was higher than in other studies. 60 This higher rate might be due to the fact that the sample we investigated was younger than the usual workforce samples and the fact that age was positively related to health issues. [88][89][90] In our analyses, we followed Navarro et al.'s (2018) 58 recommendation to separately identify the SP prevalence for the subsample of individuals who reported some kind of illness and were thus able to show SP.
Hence, the rates increased by more than 35-40%. This increase was lower than in the study by , 58 who reported SP rates of 23% for the complete sample and a rate that was more than doubled for those with health problems (53%). However, in our survey, SP levels were much higher. The distinction between SP rates for the complete sample and the subsample of those who experienced health problems provides answers to two separate questions. The first (the whole sample) indicates the economic significance of the problem, whereas the second (the subsample) can provide HRM and corporate health management with relevant information as to how many employees need support and what kinds of measures might be helpful. 90 91 Therefore, both methods of calculation are useful; however, in terms of health interventions, it is more appropriate to consider the part of the workforce reporting some kind of illness. 58 90 91 The presenteeism propensities for school and work were identical, which means that participants' decision making did not differ between the two settings. Propensities showed that on average, in 2  32 and an Austrian study reported a propensity of .59, also for employees. 60 The propensities found in the current study for students appeared to be slightly higher (.67 and .68). This finding seems to contradict the focus on work-life balance that has been reported for the generation of Millennials. 41 43 92 93 The high levels of presenteeism propensity might be explained by students who might be worried that they will not be able to keep up if they miss too many classes. 94 With regard to their jobs, the high level might be due to their work conditions, that is, most of them are probably paid on an hourly basis with the consequence that they will not earn anything if they call in sick. A more detailed view of the data revealed that the proportion of participants who always decided for SP when they were sick was more than three times higher than those who always chose SA. Millennials' attributes and expectations offer further potential explanations for their high attendance rates. 95 Millennials favor close relationships at work 96 and prefer team work inter alia in order to avoid risks. 94 Furthermore, they are interested in the acquisition of skills. 97 Thus, their decision to embrace presenteeism might reflect their desire not to let down team members (either at school or at work) and to expand their competencies. 87 Future studies should investigate whether this high propensity is due to differences in "jobs" (i.e., studying full time and working part time versus working full time) or due to different generations. We suggest that a survey be administered to full-time employees who belong to the generation of Millennials.
The high correlation between SP at school and SP indicates that both kinds of behavior are determined by individuals' health status, which is reflected in the number of days they were sick and the positive correlation with their subjective assessment of their health. Miraglia and Johns (2016) 3 found that individuals with poorer general health exhibited more presenteeism because the sheer number of health events was higher, a finding that was supported by the data in the current study. In In our correlational analyses, SP was positively associated with good subjective health and an external locus of control and negatively correlated with occupational self-efficacy. The correlation between SP and subjective health status has been well established. 65 In addition, the age-and sexadjusted multiple linear regressions with the two most important correlates (i.e., subjective health and locus of control) revealed that subjective health is a significant predictor for SP in both contexts.
This means the better participants perceive their health the more SP they report. This has to be taken into consideration in future measures to manage SP. There is only one earlier study we know of that investigated the relation between health locus of control and presenteeism among employees in all age groups, and it found lower SP for people with an internal health locus of control. 98 Although we measured general locus of control, we found the same pattern: that is, a higher SP rate for individuals with an external locus of control. Research has shown that university students score higher on internal locus of control than on external locus of control 78 and that an internal locus of control and a high level of self-efficacy 99 are associated with academic achievement. 75 Thus, students with an external locus of control might worry that they will miss too much if they do not attend classes when they are ill. Self-efficacy has been postulated to be associated with SP. 2 81 A study involving a sample of Chinese full-time workers established a positive correlation between SP and self-efficacy and found that self-efficacy could buffer the negative effect of SP on health. 82 By contrast, in our study, participants with low occupational self-efficacy showed higher levels of SP. The difference in findings may have occurred because Lu et al. (2014) 82 measured general self-efficacy, whereas we used occupational self-efficacy. In addition, research has shown that Millennials are high in self-efficacy, 93 95 and thus, they might be convinced that they can manage to make up any work they miss when they miss school or work when they are sick. By contrast, participants with low occupational self-efficacy are not sure whether they have the necessary competencies to meet expectations and thus opt for SP in order to work as much as possible and 18 meet their work and study goals. In the future, it would be interesting to investigate these contradictory results.

Strengths and weaknesses
Pertaining to the goal of the study to investigate SP among the generation of Millennials, a strength of the survey is that it provided information about the SP behavior of the future workforce, a group that has rarely been investigated with regard to SP. In addition, to our knowledge, the study is one of the first to explore SP among students who belong to the generation of Millennials. Further, since many of the participants were not just studying but were also working part time, this study allowed us to assess SP behavior in university and work settings at the same time and to compare them.
However, it is obvious that the sample was restricted to students and thus does not allow generalizations about manifestations of SP behavior among full-time employees in these birth cohorts. Additional advantages of the study are that we calculated propensities and made a distinction between individuals with and without health problems. In most studies to date, participants have been asked to quantify the number of times they have engaged in SP but not the number of times they have engaged in SA or the total number of health events they have experienced. Thus, the prevalence of SP could be reported only for the complete sample.
Shortcomings of the survey pertain mostly to methodological issues: Because we applied a crosssectional design, we were not able to identify the direction of the influence between subjective health and SP. Another weakness is that all measures were self-reports, and thus, their reliability might suffer from common method bias and overreporting due to social desirability. 65 Due to missing data and the non-applicability of questions, some of the analyses were restricted to a much smaller number of participants than the total sample size. In addition, as in many other studies, 3 participants were asked to recall incidents of sickness presence and absence over a one-year period, and therefore, the data might be biased by false recollection. 100 However, because the self-reported measure of days of sickness 100

Conclusion
The study's results are in accordance with recent findings that the prevalence of SP is continuously rising, 102 which means the issue will remain an important one. Further, they indicate that especially subjective health is associated with presenteeism behavior of Millennials. SP and the associated risks are not restricted to the current workforce but are prevalent among those who are currently enrolled in a university. One should think about implementing health education concerning SP for students who represent the future workforce and soon-to-be managers in order to sensitize them to the management of SP before they join the full-time workforce. A future study should be conducted in order to compare the results of this survey of Millennials attending a university with full-time working Millennials. Further, presenteeism propensity is important for gaining insights into individuals' decisions to engage in presenteeism or absenteeism when ill. With regard to methodology, future studies should make a distinction in prevalence rates between the complete workforce and those with health problems because these two rates provide answers to different questions.

Funding
This research received no specific grant from any funding agency in the public, commercial, or notfor-profit sectors.

Conflicting interests
None declared.

Ethics approval
The study was approved by the ethics commission of the German Society for Psychology (DGPs).

Informed consent
Participants gave informed consent before taking part in the survey and could withdraw their participation at any time.

Data sharing statement
Data are available. Please contact corresponding author.

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Millennials: Sickness presenteeism and its correlates -A cross-sectional online survey
Abstract Objective: Sickness presenteeism (SP) is a well-documented phenomenon in the current workforce.
However, little is known about the SP of future employees (Millennials). We investigated rate and propensity of presenteeism and health-and work-related correlates in university students to obtain information about the relevance of SP in the future work force.
Design and setting: We administered a cross-sectional online survey in August 2018 involving selfassessments of health-and work-related behavior. As planned, we analyzed rates, instances, and propensities of presenteeism and absenteeism. The target population was Millennial university students.

Conclusions:
The SP rates of the future work force were in line with previous research on older employees, whereas the presenteeism propensities we found here were higher. Across all analyses, subjective health proved to be associated with presenteeism. Thus, the relevance of SP will remain constant or might even increase with regard to the future workforce. Programs offering health education should be implemented to sensitize this generation as early as possible.

Introduction
Sickness presenteeism (SP) refers to going to work while ill. 1 The study of SP has gained in importance during the past two decades due to its association with sickness absenteeism, productivity, health, and attitudes. 2  productivity loss 13 and a decline in work attitudes. 14 15 Considering consequences for the employing organization, there is empirical evidence for uncovered costs caused by productivity loss. 16 SP has been reported independently of a variety of sociodemographic variables 1 17-23 and for various kinds of professional groups. 17 19 24-29 SP is a global phenomenon. Its prevalence has been documented in many countries in Europe, 17 25 29 30 the U.S., 31 Canada, 32 33 Asia, 34 and the Middle East. 35 The presenteeism rates reported for study samples vary from 30% to more than 90%.
Due to the wide range of negative effects of SP for individuals and organizations as well as the global ubiquity of SP, the study of SP seems advisable. However, although SP rates are well documented for the current workforce, the majority of which belong to the generations of Baby Boomers and Generation X, 36 37 empirical evidence concerning the SP behavior of the future generation of workers is scarce. [38][39][40] Matsushita and colleagues (2011) 39 developed an instrument to measure presenteeism among students, but they did not report on presenteeism behavior. Johansen (2018) 38 analyzed motives for the presenteeism of students in secondary school. To our knowledge, the study by   40 is the only one to date to investigate the presenteeism behavior of students. They did not find any differences in prevalence rates between medical students and STEM students and reported higher levels of presenteeism for female than for male students.
However, the prevalence rate they reported could not be compared with other studies because their way of measuring and aggregating presenteeism behavior was uncommon. Current university students are predominantly classified as Millennials, 36 41 who are said to have different attitudes  42 and they hold a "work-to-live" attitude with a higher priority on work-life balance 41 43 than previous generations. Especially this latter trend suggests that presenteeism among Millennials should be lower than among older generations. In general, interests and work values are relatively stable 37 and are associated with behavior. Thus, knowledge about the SP-related behaviors of current students should be useful for evaluating the significance and consequences of such behaviors for individuals, organizations, [44][45][46][47][48][49][50][51][52] and society in the future. [53][54][55][56][57] Specifically, we wanted to know how common presenteeism is among students belonging to the generation of Millennials and whether they favor presenteeism over absenteeism when they are sick. We were particularly interested in the question of whether they differ in their behavior with regard to study and work times and whether their behavior is associated with other health-related variables. To investigate this, we conducted an online survey.
When studying presenteeism, two methodological issues need to be borne in mind: Previous studies have usually not differentiated between individuals suffering from health events-who are thus able to show SP-and individuals without health problems-who per definition cannot show SP behavior. 58 Therefore, these studies have provided information about the prevalence of SP in the workforce but not about the prevalence among sick employees. In addition, it is necessary to distinguish between SP rates and SP propensity. 59 SP rates are measures of the frequency of attending work while ill. They depend on the number of health events and are an indicator of health status or vulnerability to illness. 60 SP propensity is the percentage of days worked while ill over the total number of days that the person was sick, 32 and it reflects an individual's probability of opting for sickness presence rather than sickness absence in the case of illness. 60 Thus, it offers additional information with regard to the decision-making process of the individual. Both aspects were considered in the current study.

Study design and population
Based on Krejcie and Morgan's (1970) 61 specifications for the calculation of a representative sample, we calculated a required sample size of 384 by taking into account a confidence interval of two standard deviations, the degree of accuracy of 0.05, and a total population of 2.9 million students in Germany. 62 During the 2018 summer term, we asked 15 random German institutions of higher education if they would allow us to send our survey to their students. Of these, four institutions agreed to forward the survey. In the email that we sent to the students, we asked participants to forward the survey to other potentially interested persons, which led to a further distribution of the survey and thus in total, students from nine German institutions of higher education took part in the online survey. Participants were informed that the survey was anonymous and voluntary and that they could withdraw their participation at any time. Of the 1,291 individuals who began taking the online survey, 791 provided complete data.

Measures of presenteeism and absenteeism
Because many students do not only study full time but are also employed in paid part-time jobs to contribute to their living, we collected data on presenteeism and absenteeism separately for school and work. To measure SP frequency, students were asked how often during the past twelve months they went to classes when the state of their health would have justified staying home. 1 9 63 The same question was posed for going to work. Whereas fixed response categories such as "never," "once," "2 to 5 times," and "more than 5 times" have been used in other studies, 1 30 63 64 we used an openquestion format. The reason for this was that the former is seen as too crude for such a low base rate behavior and might convey information about what is perceived as normal and might thus bias the answers. 65 Sickness absence (SA) was also measured with two items asking students to indicate how often during the past twelve months they stayed home due to sickness instead of going to classes/work.  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59 [68][69][70][71][72][73] Self-efficacy is one's belief in one's competence to perform intended actions. Efficacy beliefs influence the self-regulation of motivation through goal challenges and outcome expectations and the types of activities people choose. 74 Selfefficacy and locus of control (especially health locus of control) are seen as personal health resources that determine health-related behavior. 73 Both concepts have repeatedly been used in studies of the health-related behaviors of students. 73 75-78 In addition, we thought the extent of paid work would be a relevant correlate because it is an indicator of workload, which is known to be related to presenteeism. 3 With regard to students' health status, we used two variables based on a sequence of subjective assessments. Subjective health status was calculated as the mean of two items ("How do you rate your general susceptibility to disease?"; "How do you rate your health in comparison with your age group?"). The scale was a slider ranging from 0 ("very low"; "very bad") to 100 ("very high"; "very good"). We used the 4-item short scale by   79 to measure locus of control (e.g., "When I really try, I will succeed") and three items from the short scale of occupational self-efficacy 80 (e.g., "I am not sure I have all the abilities necessary for my job"). Both locus of control and  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60   F  o  r  p  e  e  r  r  e  v  i  e  w  o  n  l  y   8 occupational self-efficacy are stable characteristics that are relevant to presenteeism. 65 81 82 Response categories for the seven items ranged from 1 ("does not apply at all") to 5 ("fully applies").

Employment and demographic variables
Participants stated whether they had worked before they started their university program, and they were asked if and how many hours they worked while attending school and during semester breaks.
The survey asked for demographic information on gender, age, study major, pursued degree, and name of university. Employment and demographic variables were measured with one item each.

Data analysis
The number of health events was calculated as the sum of the SP and SA frequencies. 33 60 We computed presenteeism propensity as SP frequency divided by the number of health events for university and work settings separately. Hence, SA propensity was 1-SP propensity. 60 1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60   F  o  r  p  e  e  r  r  e  v  i  e  w  o  n  l  y   9 because some of the questions did not apply to all participants (e.g., those referring to working while studying). Thus, analyses of subgroups differed in sample sizes. Participants who had missing data on one of the investigated variables were excluded from the respective analysis.

Ethics approval and informed consent of participants
The study was approved by the ethics commission of the German Society for Psychology (DGPs).
Before beginning the study, participants were informed that their participation was voluntary and that they could withdraw their participation at any time while working on the questionnaire. They were informed that no personalized data would be collected, that their data would be used for scientific purposes only, and that it would be stored and analyzed anonymously so that it would not be possible to establish any connection between them and their answers.

Patient and public involvement
Neither subjects nor public were involved in the study.

Results
A total of 791 questionnaires were completed. In accordance with the goal of the study, the analyses were restricted to participants belonging to the generation of interest, the Millennials, which include people who were born in 1981 or later. 36 41 Further, cases of long-term absence or presence were excluded from the analyses because these were likely to have been caused by different modalities. 60 As was done in other studies, we defined 60 days as the threshold. 60 1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  Not specified 578 32.6 104 13.9 * Participants included in the analyses were those who completed the questionnaire and belonged to the generation of Millennials Sickness. The descriptive results for the number of days of sickness in the past twelve months can be found in Table 2 and the correlations with other factors in Table 3. It turned out that participants who worked while attending school reported a significantly larger number of days of sickness during school time than during work time. Further, the correlation between days of sickness during school  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59 1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60   F  o  r  p  e  e  r  r  e  v  i  e  w  o  n  l  y   12 during the past twelve months were able to show presenteeism (see Table 4, right side). As results show, 72.8% of the sample were left for analyses regarding SP at school (n=545) and 69.7% with regard to work (n=468). Therefore, after excluding "healthy" participants, the SP rates rose to 87.9% during school time and 87% during work time. Correlates of SP: With regard to SP at school, we found a significant correlation with SP at work (Rho=0.49, p=0.000). Further correlations for SP during school and work time are listed in Table 5.  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60   F  o  r  p  e  e  r  r  e  v  i  e  w  o  n  l  y   13 In order to further investigate the two most important correlates, we computed multiple linear regressions using ordinary least square method and variables selection method "Enter" (consideration of both variables). Linearity, multicollinearity and homoscedasticity. First, we checked for whether the assumptions for the application of the method were fulfilled. 84 Data were collected through independent random sampling. Inspection of scatterplots of the independent variables against the dependent and unstandardized predicted values against studentized residuals indicated that the assumption of linearity between independent and dependent variables was met. In addition, the assumptions with respect to homoscedascity and multicollinearity were met. Outliers were identified in two ways. First, all subjects with values above or below three standard deviations of studentized deleted residuals were eliminated from the analyses. Second, on the basis of the leverage index, all subjects with values above the critical value (i.e., 2*p/n) 85 were excluded from the analyses. Thus, 419 subjects were left for the analysis of presenteeism at school and 323 subjects for the analysis of presenteeism at work (Table 6).  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  The probability of going to classes when sick was significantly higher than the probability of staying home (Z(544)=-10.042, p=0.000). With regard to work time, the pattern was quite similar: The probability of going to work while ill was significantly higher than the probability of staying home (Z(467)=-9.444, p=0.000). There were no gender differences in presenteeism propensity during school or work time.

Discussion
Aim of the survey was to obtain information about the presenteeism behavior of studying Millennials who constitute the future workforce. While more than one fourth of participants reported no incidents of sickness during the past year, those who reported at least some kind of illness reported a  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60   F  o  r  p  e  e  r  r  e  v  i  e  w  o  n  l  y   15 were highly associated. Further, SP was positively correlated with good subjective health and an external locus of control and negatively correlated with occupational self-efficacy. Across all analyses, including multiple linear regressions, subjective health was the variable with the strongest association with SP. Results of the study show that the relevance of SP will remain constant or might even increase with regard to the future workforce.
In this survey, SP rates for the complete sample were on an average level in comparison to recent research among German employees that has reported great variability in rates ranging from 35% 86 to more than 90%. 87 The levels found here were in the same range as studies that were conducted with employees in the Netherlands, 28 Scandinavia, 87 and other European countries. 23 The proportion of participants who reported no health event during the past year was higher than in other studies. 60 This higher rate might be due to the fact that the sample we investigated was younger than the usual workforce samples and the fact that age was positively related to health issues. [88][89][90] In our analyses, we followed Navarro et al.'s (2018) 58 recommendation to separately identify the SP prevalence for the subsample of individuals who reported some kind of illness and were thus able to show SP.
Hence, the rates increased by more than 35-40%. This increase was lower than in the study by , 58 who reported SP rates of 23% for the complete sample and a rate that was more than doubled for those with health problems (53%). However, in our survey, SP levels were much higher. The distinction between SP rates for the complete sample and the subsample of those who experienced health problems provides answers to two separate questions. The first (the whole sample) indicates the economic significance of the problem, whereas the second (the subsample) can provide HRM and corporate health management with relevant information as to how many employees need support and what kinds of measures might be helpful. 90 91 Therefore, both methods of calculation are useful; however, in terms of health interventions, it is more appropriate to consider the part of the workforce reporting some kind of illness. 58 90 91 The presenteeism propensities for school and work were identical, which means that participants' decision making did not differ between the two settings. Propensities showed that on average, in 2  32 and an Austrian study reported a propensity of .59, also for employees. 60 The propensities found in the current study for students appeared to be slightly higher (.67 and .68). This finding seems to contradict the focus on work-life balance that has been reported for the generation of Millennials. 41 43 92 93 The high levels of presenteeism propensity might be explained by students who might be worried that they will not be able to keep up if they miss too many classes. 94 With regard to their jobs, the high level might be due to their work conditions, that is, most of them are probably paid on an hourly basis with the consequence that they will not earn anything if they call in sick. A more detailed view of the data revealed that the proportion of participants who always decided for SP when they were sick was more than three times higher than those who always chose SA. Millennials' attributes and expectations offer further potential explanations for their high attendance rates. 95 Millennials favor close relationships at work 96 and prefer team work inter alia in order to avoid risks. 94 Furthermore, they are interested in the acquisition of skills. 97 Thus, their decision to embrace presenteeism might reflect their desire not to let down team members (either at school or at work) and to expand their competencies. 87 Future studies should investigate whether this high propensity is due to differences in "jobs" (i.e., studying full time and working part time versus working full time) or due to different generations. We suggest that a survey be administered to full-time employees who belong to the generation of Millennials.
The high correlation between SP at school and SP indicates that both kinds of behavior are determined by individuals' health status, which is reflected in the number of days they were sick and the positive correlation with their subjective assessment of their health. Miraglia and Johns (2016) 3 found that individuals with poorer general health exhibited more presenteeism because the sheer number of health events was higher, a finding that was supported by the data in the current study. In  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60   F  o  r  p  e  e  r  r  e  v  i  e  w  o  n  l  y   17 addition, the positive correlation between SP and SA also found here has been well established, 1 6 17 21 63 65 although it seemed particularly high in this study.
In our correlational analyses, SP was positively associated with good subjective health and an external locus of control and negatively correlated with occupational self-efficacy. The correlation between SP and subjective health status has been well established. 65 In addition, the age-and sexadjusted multiple linear regressions with the two most important correlates (i.e., subjective health and locus of control) revealed that subjective health is a significant predictor for SP in both contexts.
This means the better participants perceive their health the more SP they report. This has to be taken into consideration in future measures to manage SP. There is only one earlier study we know of that investigated the relation between health locus of control and presenteeism among employees in all age groups, and it found lower SP for people with an internal health locus of control. 98 Although we measured general locus of control, we found the same pattern: that is, a higher SP rate for individuals with an external locus of control. Research has shown that university students score higher on internal locus of control than on external locus of control 78 and that an internal locus of control and a high level of self-efficacy 99 are associated with academic achievement. 75 Thus, students with an external locus of control might worry that they will miss too much if they do not attend classes when they are ill. Self-efficacy has been postulated to be associated with SP. 2 81 A study involving a sample of Chinese full-time workers established a positive correlation between SP and self-efficacy and found that self-efficacy could buffer the negative effect of SP on health. 82 By contrast, in our study, participants with low occupational self-efficacy showed higher levels of SP. The difference in findings may have occurred because Lu et al. (2014) 82 measured general self-efficacy, whereas we used occupational self-efficacy. In addition, research has shown that Millennials are high in self-efficacy, 93 95 and thus, they might be convinced that they can manage to make up any work they miss when they miss school or work when they are sick. By contrast, participants with low occupational self-efficacy are not sure whether they have the necessary competencies to meet expectations and thus opt for SP in order to work as much as possible and  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60   F  o  r  p  e  e  r  r  e  v  i  e  w  o  n  l  y 18 meet their work and study goals. In the future, it would be interesting to investigate these contradictory results.

Strengths and weaknesses
Pertaining to the goal of the study to investigate SP among the generation of Millennials, a strength of the survey is that it provided information about the SP behavior of the future workforce, a group that has rarely been investigated with regard to SP. In addition, to our knowledge, the study is one of the first to explore SP among students who belong to the generation of Millennials. Further, since many of the participants were not just studying but were also working part time, this study allowed us to assess SP behavior in university and work settings at the same time and to compare them.
However, it is obvious that the sample was restricted to students and thus does not allow generalizations about manifestations of SP behavior among full-time employees in these birth cohorts. Additional advantages of the study are that we calculated propensities and made a distinction between individuals with and without health problems. In most studies to date, participants have been asked to quantify the number of times they have engaged in SP but not the number of times they have engaged in SA or the total number of health events they have experienced. Thus, the prevalence of SP could be reported only for the complete sample.
Shortcomings of the survey pertain mostly to methodological issues: Because we applied a crosssectional design, we were not able to identify the direction of the influence between subjective health and SP. Another weakness is that all measures were self-reports, and thus, their reliability might suffer from common method bias and overreporting due to social desirability. 65 Due to missing data and the non-applicability of questions, some of the analyses were restricted to a much smaller number of participants than the total sample size. In addition, as in many other studies, 3 participants were asked to recall incidents of sickness presence and absence over a one-year period, and therefore, the data might be biased by false recollection. 100 However, because the self-reported measure of days of sickness 100 1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60   F  o  r  p  e  e  r  r  e  v  i  e  w  o  n  l  y   19 level of correspondence with objective data, we used the self-report method as a practicable way to obtain the relevant data.

Conclusion
The study's results are in accordance with recent findings that the prevalence of SP is continuously rising, 102 which means the issue will remain an important one. Further, they indicate that especially subjective health is associated with presenteeism behavior of Millennials. SP and the associated risks are not restricted to the current workforce but are prevalent among those who are currently enrolled in a university. One should think about implementing health education concerning SP for students who represent the future workforce and soon-to-be managers in order to sensitize them to the management of SP before they join the full-time workforce. A future study should be conducted in order to compare the results of this survey of Millennials attending a university with full-time working Millennials. Further, presenteeism propensity is important for gaining insights into individuals' decisions to engage in presenteeism or absenteeism when ill. With regard to methodology, future studies should make a distinction in prevalence rates between the complete workforce and those with health problems because these two rates provide answers to different questions.

Author Contributions
DL and FR contributed to the conception and design of the study as well as to the collection and assembly of the data. DL and FR contributed to the statistical analysis, the interpretation of the data, and the drafting of the manuscript.

Funding
This research received no specific grant from any funding agency in the public, commercial, or notfor-profit sectors.

Conflicting interests
None declared.

Ethics approval
The study was approved by the ethics commission of the German Society for Psychology (DGPs).

Informed consent
Participants gave informed consent before taking part in the survey and could withdraw their participation at any time.

Data sharing statement
Data are available. Please contact corresponding author.

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In your methods section, say that you used the STROBE cross sectional reporting guidelines, and cite them as: Statistical methods #12a Describe all statistical methods, including those used to control for confounding [8][9] #12b Describe any methods used to examine subgroups and interactions 8-9 #12c Explain how missing data were addressed 8-9 #12d If applicable, describe analytical methods taking account of sampling strategy n/a #12e Describe any sensitivity analyses n/a Participants #13a Report numbers of individuals at each stage of study-eg numbers potentially eligible, examined for eligibility, confirmed eligible, included in the study, completing followup, and analysed. Give information separately for for exposed and unexposed groups if applicable.

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