{'fraction_non_alphanumeric': 0.03931699094939724, 'fraction_numerical': 0.022351691033674105, 'mean_word_length': 5.091964285714286, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Using text message reminders in health care services: A narrative literature review

Introduction Despite the extensive use of mHealth behavior change interventions, questions remain about the use of technology-based reminders in delivering health care services. Text messaging, or short message service (SMS), is one reminder method that has been extensively researched. Most SMS-reminder research is distributed across a range of health care outcomes. The aim of this article is to systematically review the aggregate impact of these reminders on overall health care outcomes. Methods A systematic literature review was conducted and yielded 2316 articles. Studies were included if they used SMS reminders to support patient health care outcomes. Study methodology was aligned with the PRISMA guidelines for systematic reviews. Results Following screening, 162 articles met inclusion criteria. Of these studies, 93 investigated medical compliance reminders and 56 investigated appointment reminders. The review found that nearly all the SMS-reminder studies helped improve patient medical compliance and appointment reminders. Additionally, researchers reported numerous benefits from using SMS reminders, including ease of use, relative inexpensiveness, and rapid and automated message delivery. Minimal risks were reported and most participants found the reminders to be acceptable. Discussion Text messages appear to be an effective reminder mechanism to promote improved patient appointment and medical compliance. Reminders should continue to be evaluated and improved to determine the most effective timing and frequency of messages for improving outcomes.


Introduction
In 2017, there were an estimated 7.7 billion mobile phones used, approximately one phone per person on the planet (International Telecommunication Union, 2017). Mobile phones, and more recently smartphones, have quickly changed the way people communicate and the way treatment providers think about service delivery (Atun and Sittampalam, 2006). Mobile phones are used in a variety of settings for various purposes, including in impoverished countries where mobile phones offer a relatively inexpensive method of communication (Ben-Zeev et al., 2015;Free et al., 2010); for treating individuals with psychological problems (Thomas et al., 2017); and for routine communication among individuals of all ages (Center for Substance Abuse Treatment, 2009;Global Attitudes Project, 2012). Due to the ubiquity of text messaging (short message service, SMS) (Gatwood et al., 2016), customizability (e.g., Downer et al., 2005), relative low cost (e.g., Rohman et al., 2015), rapid and automated delivery (e.g., Chung et al., 2015), and acceptability (Garofalo et al., 2016), SMS has become a focus of researchers in the health care field and is recommended for use by leading organizations in various health care fields (e.g., American Medical Association, 2016; World Health Organization, 2012). Nevertheless, SMS is a relatively nascent technology. Using it in research requires continuous researcher education on ever-changing SMS treatment guidelines and implementation methods, and frequent training of research staff that help implement the rapidly evolving interventions.
Research on SMS in health care services has been focused on two main areas: behavior change interventions and reminders. Mobile Health (mHealth) is defined as the use of mobile computing and communication technologies in health care and public health (Berrouiguet et al., 2016;Free et al., 2010). Behavior change interventions and reminders both fall under the umbrella of mHealth. Although mHealth reminder research has primarily focused on outcomes such as appointment attendance and medication adherence (Berrouiguet et al., 2016;Kannisto et al., 2014), SMS reminders can also play an important role in behavior change. As proposed in the transtheoretical model of change, reminders can serve as coaching or prompts to help facilitate behavior change (Prochaska et al., 1994). They are likened to stop signs at a busy intersection-reminding us how to respond next. Reminders can be used to enhance prospective memory, which is remembering to complete an activity in the future (Guynn et al., 1998;McDaniel et al., 2004).
Before the cell phone era, Prochaska et al. (1994) highlighted the utility of alarm clocks, calendars, and timers as tools for delivering personal reminders. These tools are now easily and frequently accessed from one source: the mobile phone (Madden et al., 2013;Nelson and Nelson, 2010). Mobile phones can receive automated SMS reminders or notifications that remind the user to do (or not to do) a specific behavior. For example, if an individual is attempting to decrease their substance use, they can receive an automated SMS that reminds them of their goal at certain high-risk times; and if an individual is attempting to lose weight, they can receive a reminder not to snack between meals. Recently, some research has begun to investigate the impact of adjunct reminders (i.e., mHealth reminders as an adjunct to a behavior change intervention) (e.g., Aguilera et al., 2017). Due to the paucity of research on adjunct reminders at this time, they will not be included as part of the systematic review. However, this topic is covered in the Discussion section. The current review will address the following questions about the use of mHealth reminders in health care: What specific uses mHealth reminders been applied to in health care? How has the impact of mHealth reminders been assessed? What have we learned about designing reminders for health care? The review methodology has been aligned with the PRISMA guidelines for systematic reviews (Moher et al., 2009).

Objective
The objective of this study is to provide a systematic narrative review of the application of SMS reminders in health care services. All studies were categorized using a two-step process. First, all the titles and abstracts were reviewed for relevance to the topic and to see if they met inclusion criteria. Second, the studies were read and categorized by methodology, treatment goal, and target health condition.

Search strategy
An extensive literature search was conducted in April 2018 using the PsychINFO, CINAHL, PubMed, and Web of Science electronic databases. The search terms used were selected to broadly examine the impact of text message reminders on health care outcomes (see Fig. 1). Titles, abstracts, and reference lists of the selected studies were also reviewed to check for other potentially relevant studies.

Selection criteria
The review was limited to peer-reviewed articles published in English between 2003 and 2018, with an abstract available online. The starting date of the search was selected for three reasons: (1) the majority of mHealth research has occurred after 2003, (2) the rate of text messaging and cell phone ownership has greatly increased since 2003 (International Telecommunication Union, 2017;Kannisto et al., 2014), and (3) 2003 is a typical beginning date for mHealth literature reviews (Berrouiguet et al., 2016;Kannisto et al., 2014). The review was limited to studies of SMS reminders used to support patient health care. While the majority of studies sent SMS directly to the patients, some health care needs necessitate the reminders be sent to guardians or caretakers rather than the patient. There was no limitation on patient population, age, or diagnosis. Excluded from this review were: articles that assessed patients' feelings toward SMS for non-clinical purposes (e.g., to create a list of SMS messages or assess expected acceptability of receiving messages), theoretical papers, statistical reviews, dissertations, editorials, letters, and study protocols. Both randomized control trials (RCTs) and non-RCTs (e.g., feasibility studies, before-and-after studies, crosssectional studies, cohort studies) were included.

Study selection
The steps illustrating the literature search and article review process are shown in Fig. 1. The initial search produced 2316 articles. An additional 62 articles were found by looking at the reference list of each article. After checking for duplicates as well as screening titles and abstracts for relevance to the topic, 196 potential full-text articles were obtained, with 162 articles ultimately meeting inclusion criteria after full-text review.

Characteristics of studies reviewed
Author, year, country, research setting, type of study, patient group, sample size, and message dose (i.e., timing of messages, frequency of messages, total number of messages) were extracted to describe the characteristics of the study. These results have been summarized in Table 1. The number of articles published on this topic has gradually increased over time, peaking in 2015 (35/162; 22%). Approximately one-third of the studies reviewed were conducted in the United States (60/162; 37%).
Nearly two-thirds (111/162; 68%) of the studies reviewed were randomized control trials (RCTs), with a marked increase in RCTs after 2013. Non-RCTs were recorded as quasi-experimental. Additional descriptive characteristics of the studies are presented in more detail in Table 1.

Purposes of text message reminders in health care treatment
The reported purpose of the study, description of the intervention, and dose of the intervention were extracted to describe the most commonly studied application of mHealth reminders in health care. SMS reminders were primarily used to remind patients to comply with a medical practice (e.g., taking medication on time, following non-medical treatment guidelines, and completing vaccinations) (93/162; 57%) or attend a clinical appointment (56/162; 35%). Reminders for appointment attendance were generally used as a method to increase clinical appointment attendance and the rate of advance cancellations (as opposed to not showing up). Various studies assessed the impact of SMS reminders on decreasing the rate of missed appointments across a variety of settings, including first-time psychotherapy appointments (Clough and Casey, 2014), recurring medical appointments (Branson et al., 2013;Tolonen et al., 2014), and completing vaccinations (Stockwell et al., 2014).
In a majority of studies (140/162; 86%), SMS reminders were the only intervention used. The remaining studies used a secondary or complimentary component in conjunction with the SMS reminder. These include educational or informational messages about the treatment target (e.g., Stockwell et al., 2014), links to additional educational information (e.g., Kodama et al., 2016), phone call reminders and/or mailed reminders (e.g., Baker et al., 2015), and motivational or supportive messages (e.g., Celik et al., 2015).

Message dosage and timing
Across the studies, it was most common that the dose (number) and timing of messages were individually customized based on the patients' medication or treatment schedule, or scheduled appointments. Other studies used researcher-selected dosing (Belton et al., 2013;Odeny et al., 2014). Many studies sent daily or weekly messages, however, not all studies reported details about message timing. Some studies set message dosage based solely on patient preference (e.g., Spohr et al., 2015), and others reported the total amount of reminders sent rather than when they were sent (e.g., Celik et al., 2015).
Specific timing of reminders varied across studies. Detailed timing (e.g., a specific time or time frame) was reported in 75 of 162 (46%) of the studies reviewed. Medication reminders typically were sent near the scheduled medication time (e.g., Mao et al., 2008). Specific appointment reminder time was reported in 86% (49/57) of studies. These reminders occurred between two weeks (Kunigiri et al., 2014) and the morning of (Prasad and Anand, 2012) a scheduled appointment. Additionally, studies reminding individuals to complete a medical followup exam sent a reminder message up to six months after initial contact (Van Ryswyk et al., 2015).
Six of the eight studies that did not find improved outcomes for individuals receiving SMS reminders reported neutral results. Of the six studies, one reported being underpowered to assess appointment attendance differences (Fischer et al., 2012); two found no significant difference between a phone call, mailed, and SMS reminder (Bos et al., 2005;Kunigiri et al., 2014); one found no significant difference between a mailed reminder and a mailed reminder in addition to a SMS reminder (Delgadillo et al., 2015); one found no significant difference between a SMS reminder and no SMS reminder (Bellucci et al., 2017); and one found no significant difference between a telephone call and a SMS reminder (Junod . The seventh study (Clough and Casey, 2014), found SMS appointment reminders were not significantly more effective than the control group at increasing intake appointment attendance at an outpatient training clinic. The results trended toward more participants receiving reminders dropping out before their intake appointment. Despite this, the authors still suggest that with further research SMS may prove to be a viable appointment reminder system. The eighth study (Nelson et al., 2011) found that phone reminders were more effective than SMS reminders at increasing pediatric dental appointment attendance. Despite this, the authors suggested continuing to investigate the effectiveness of messages based on patient preference (i.e., sending text messages to individuals that prefer them as a reminder method). Kunigiri et al. (2014) found SMS reminders were not statistically significantly more effective than calls or mailed reminders. Yet, they suggest continuing to use SMS messages as an appointment reminder mechanism due to its ease and relative inexpensiveness.
Of the 14 studies that did not find a positive improvement, all but one reported the intervention had a neutral effect on participants. Three of the studies found that despite the medical compliance reminders not being more effective than the control group, the reminders still had benefits, including increasing medical knowledge (Richman et al., 2016), increasing self-efficacy in disease self-management (Gatwood et al., 2016), and increasing the rate of consecutive days taking medication (Stoner et al., 2015). Two of the studies reported being unpowered to find a statistically significant difference (Boker et al., 2012;Buis et al., 2017). Niederhauser et al. (2015) reported that their experimental group had more barriers to immunization than control and hypothesized that with a larger trial they might expect to find statistically significant results. One study reported most of their control group used their own reminder, potentially confounding the non-significant outcomes (Hou et al., 2010), and a second study hypothesized that many participants in the control group used their own reminder (although this was not formally assessed) (Mbuagbaw et al., 2012). Another study found that a phone call reminder was more effective than a SMS reminder at increasing treatment follow-up appointment completion (Porto-Ferreira et al., 2017). Two studies found both the treatment and control group had a significantly higher medication adherence and appointment attendance rate than typical (Burton et al., 2014;Goldstein et al., 2014); and another hypothesized that due to the length of their study, the novelty and benefit of a medication reminder may have worn off (Ting et al., 2012). Two studies did not find that SMS reminder helped increase rate of Hepatitis B and anti-retroviral therapy (ART) medication adherence and, in fact, displayed lower rates of adherence than no reminder or treatment as usual (respectively) (Linnemayr et al., 2017;McIver et al., 2016). Lastly, all studies that included a measure of feasibility and/or acceptability found positive results (e.g., Garofalo et al., 2016;Gengiah et al., 2014;Park et al., 2014), even if the intervention was not found to be statistically significant (e.g., Buis et al., 2017;Richman et al., 2016).

Miscellaneous messages
The remaining studies (15/162; 9%) that did not meet inclusion criteria as either an appointment or medical compliance reminder are grouped below by intervention outcome and briefly described.

Tooth brushing
Two studies assessed the impact of SMS reminders on the amount of plaque and level of oral hygiene. Bowen et al. (2015) found that SMS reminders helped adolescents and young adults (ages 11 to 18) decrease the amount of plaque on their teeth. Eppright et al. (2014) found that reminders helped adolescents and young adults (ages 11 to 19) improve their level of oral hygiene. Both studies were RCTs and were conducted at outpatient University clinics in the United States.

Diabetes
One study assessed the impact of reminders on perceived diabetes knowledge and injection skill among adults (ages 18 to 75) with diabetes mellitus in Turkey. The studies found reminders were effective at increasing patient-perceived diabetes knowledge and injection skill (Celik et al., 2015).

Schizophrenia
Pijnenborg et al. (2010) found SMS reminders helped inpatients and outpatients at a University clinic in the Netherlands with schizophrenia achieve a higher percentage of goal-directed behaviors (e.g., carrying out leisure activities). The study was quasi-experimental and utilized a wait list control.

Traumatic brain injury (TBI)
Hart and Vaccaro (2017) found SMS reminders helped individuals nearing discharge from intensive outpatient brain injury treatment with a TBI in the United States to more effectively implement goal-directed behaviors (e.g., seeking out appropriate social interaction). The study was an RCT with the control group receiving treatment as usual (TAU).
3.7.6. Suicidal ideation Kodama et al. (2016) found SMS messages with informational links to social welfare services made psychiatric outpatients with high levels of suicidal ideation in Japan more likely to seek help when experiencing suicidal ideation. The study was quasi-experimental.
3.7.7. Substance use Spohr et al. (2015) found SMS reminders helped adults (ages 19 to 62) on probation in the United States maintain substance use abstinence and initiate substance use treatment while in a criminal justice setting. The study was a RCT with the control group receiving no reminders. Odeny et al. (2014) used SMS reminders to deter adult males in Kenya from resuming sexual activity too soon after circumcision. This basic intervention was not successful in reducing early resumption of sexual activity. The researchers suggest further investigation of SMS reminders should be paired with a behavioral intervention, citing the high likelihood that participants may not have understand postoperative instructions. Abroms et al. (2014) used SMS reminders to help adults (mean age: 35.7 years old) in the United States stop smoking. The study found that the interactive, personalized reminders helped individuals abstain from smoking statistically significantly more than the control group that received self-help TAU.

Discussion
The results of this literature review demonstrate SMS reminders can be effectively implemented worldwide (e.g., Chen et al., 2008) and in a variety of settings (e.g., Stockwell et al., 2014) to help improve health care services. SMS reminders show excellent promise as an automated support mechanism. The review found 86% (48/56) of appointmentreminder studies and 85% (83/97) of medical compliance reminder studies reported positive results associated with SMS messages. The reminders helped increase appointment attendance (e.g., Guy et al., 2013) and before-appointment cancellations (an unexpected outcome; e.g., Steiner et al., 2016), as well as decrease missed appointments (e.g., Altuwaijri et al., 2012). By decreasing missed appointments and increasing advance cancellations, health care providers can save time and money, maintain uninterrupted care, and allow other patients to receive needed treatment (da Costa et al., 2010;Farmer et al., 2014;Rohman et al., 2015;Ting et al., 2012). SMS reminders also helped increase the rate of medication adherence (e.g., Montes et al., 2012), non-medication treatment adherence (e.g., Balato et al., 2013), and vaccination completion (e.g., Stockwell et al., 2014).
SMS reminders showed promising results in studies of various diseases and conditions, including HIV, diabetes, heart problems, schizophrenia, skin problems, asthma, IBS, Parkinson's disease, psychosis, stroke, Hepatitis A and B, and breast cancer. A minority of studies did not find positive results. However, even these authors suggested that potential limitations such as small sample size (Fischer et al., 2012) or control group participants using their own reminders (Hou et al., 2010;Mbuagbaw et al., 2012) may have confounded the results. The review found a single study investigating each of the following: IBS, Parkinson's disease, psychosis, stroke, breast cancer, and oral contraception. Given the lack of research in these areas, further research would be helpful to better understand the impact SMS reminders can have on these particular health care problems. However, given the composite effectiveness of SMS reminders for health care problems and the initial promising results described above, it seems probable SMS reminders are effective if implemented as a reminder mechanism.

Benefits of SMS reminders
SMS messages are relatively inexpensive, easily customized, automatically sent directly to individuals, and a part of many individuals' daily life. Given these attributes, it is not surprising many studies utilize SMS as a reminder to help improve health care services. SMS can function as a reminder both for recurring (e.g., daily medication adherence) and distal, one-time (e.g., to complete a follow-up vaccination two months after initial vaccination) behaviors. Clinics report major financial savings after implementing an automated, SMS-reminder system, and attribute the savings to the relative inexpensiveness of SMS reminders and the decreased rate of missed appointments (e.g., Pratap et al., 2015;Rohman et al., 2015). SMS messages may also help individuals who need additional support or structure to remember things or to engage in a behavior (e.g., individuals with schizophrenia or a TBI) (Hart and Vaccaro, 2017;Pijnenborg et al., 2010).
Medical professionals can use technology to help guide their treatment. With technology, they can receive more accurate information about treatment adherence when they are treating patients whose recall and self-report may not be accurate (e.g., Boker et al., 2012).

Potential consequences, risks, and drawbacks of SMS reminders
Patient confidentiality is frequently cited as a risk of using SMS in health care treatment (e.g., Branson et al., 2013;Downer et al., 2005). While confidentiality is a risk, there are steps that can be taken to mitigate the concern. These steps include: sending generic reminders (e.g., "See you next Thursday at 5"); informing individuals to open messages in a private location and delete messages after reading them; and suggesting individuals use password protection on their phones. However, SMS is an inherently insecure system technology. Unless an encrypted messaging application is being used, there is a possibility that any message sent can be read by someone other than the intended recipient-a risk that most individuals take on a daily basis (willingly or unwittingly).
One drawback is individuals not reading the messages they've received. A potential strategy to mitigate the possibility of messages being ignored is to utilize interactive or two-way messaging that elicits a response from message recipients. Another drawback is the possibility that recipients may become annoyed at receiving multiple messages over time. Note that none of the studies reviewed found SMS reminders caused adverse iatrogenic results.

Future directions
SMS reminders show great promise for use across the broad scope of health care services. This review found SMS reminders are highly effective as both an appointment and medical compliance reminder. Additionally, SMS reminders were found to be effective at prompting a number of other health behaviors, including self-medical examinations, socialization, and goal-directed behaviors. As of now, it is unclear what is the most effective dose of SMS reminders (i.e., timing, frequency, and total number of messages) and under what conditions should dosage be changed over time. It is likely dosage varies between individuals and is impacted by the perceived importance of the reminder (e.g., is it for something crucial to your health or for changing a behavior you aren't particularly motivated to change?). Additionally, the underlying mechanism that makes SMS reminders effective and aid prospective memory is not understood. Further research on these topics can help inform future implementations of reminders.
There is an existing body of research on the use of SMS to deliver interventions (e.g., Haug et al., 2012). Some studies have also investigated using SMS reminders as an adjunct (e.g., receiving an appointment reminder to continue attending the main intervention) to therapy (e.g., Abroms et al., 2014). However, very few studies have investigated the effectiveness of using SMS as a supportive adjunct to behavioral health treatment. One such study (Aguilera et al., 2017) used text messages not only as a reminder, but also as a support mechanism for racial/ethnic minority patients receiving cognitive-behavioral therapy (CBT) for depression. While the study did not find a statistically significant benefit of SMS, this is an area that may require further research to better understand how to implement reminders as a prompt to help support behavior change.

Limitations
While this review draws from many diverse sources, the data were synthesized using a narrative method rather than a meta-analysis, thus the findings cannot be used to recommend a preferred strategy for the use of SMS reminders in health care. The studies varied in methodological rigor, which may have impacted their results and biased the interpretation in this review. Studies were only selected from peer-reviewed, English-language journals, which may have restricted the findings.

Conclusion
The findings for the use of SMS reminders in health care treatment are very promising. A rapidly increasing body of literature on SMS reminders demonstrates the value of using SMS reminders. The results indicate SMS reminders provide an inexpensive, easily implemented, and automatable method to help increase medical compliance and improve appointment attendance. Additionally, these results suggest SMS reminders may be helpful in improving prospective memory and supplementing behavior change interventions by reminding recipients to engage (or not engage) with behaviors they wish to change.

Declaration of conflicting interests
The authors declare that there is no conflict of interest with respect to the research, authorship, and/or publication of this article.

Funding
This work was supported by the National Institute on Alcohol Abuse and Alcoholism [grant number 1F31AA025531-01].