{'fraction_non_alphanumeric': 0.04514720248242573, 'fraction_numerical': 0.030321604382554063, 'mean_word_length': 5.037700936741066, 'pattern_counts': {'":': 0, '<': 40, '<?xml version=': 0, '>': 1, '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}}
Conduct problems and depressive symptoms in association with problem gambling and gaming: A systematic review

Abstract Background and aims Behavioral addictions such as gambling and gaming disorder are significant public health issues that are of increasing importance to policy makers and health care providers. Problem gambling and gaming behaviors have been identified as being associated with externalizing and internalizing problems, with theoretical models suggesting that both conduct problems and depressive symptoms may be significant risk factors in the development of problem gambling and gaming. As such, the purpose of this systematic review is to provide an overview of research identifying the relationship between conduct problems, depressive symptoms and problem gambling and gaming among adolescents and young adults. Methods Systematic literature searches in accordance with PRISMA guidelines found 71 eligible studies that met the inclusion criteria, 47 for problem gambling, 23 for problem gaming and one for both problem behaviors. Results Based on cross-sectional evidence, both problem gambling and gaming are consistently concurrently associated with conduct problems and depressive symptoms. Longitudinal evidence appears to be clearer for conduct problems as a risk factor for problem gambling, and depressive symptoms as a risk factor for problem gaming. However, both risk factors appear to increase the risk for these problem behaviors. Discussion and Conclusions Results from the literature review suggest that problem gambling and gaming are associated with the presence of conduct problems and depressive symptoms, with the potential of sharing common etiological factors. Additional research is necessary to confirm these longitudinal relationships with an emphasis on investigating the interaction of both early conduct problems and depressive symptoms.


INTRODUCTION
Gambling and gaming behaviors are generally described as being on a continuum ranging from occasional or recreational participation, through to problematic, excessive and disordered engagement (Griffiths, Kuss, Lopez-Fernandez, & Pontes, 2017;Shaffer & Korn, 2002). In the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5; American Psychiatric Association [APA], 2013), gambling disorder was reclassified as a nonsubstance-related disorder and Internet gaming disorder was included in Section III as a condition requiring further research (APA, 2013). Moreover, as of May 2019, the World Health Organization (WHO) officially included gaming disorder in the International Classification of Diseases -Eleventh Edition (ICD-11; WHO, 2019) alongside gambling disorder as the two formally recognized disorders due to addictive behaviors (WHO, 2019). According to the DSM-5 (APA, 2013), both disorders are defined as the persistent and recurrent engagement in the behavior (gambling or video gaming), leading to clinically significant impairment or distress. Recent research has identified that rates of problematic participation in both gambling and gaming are higher among adolescents and young adults, with 0.2-12.3% reporting problem gambling (PG; Calado, Alexandre, & Griffiths, 2017) and 5-10% reporting problem video gaming (PVG; Fam, 2018;Paulus, Ohmann, von Gontard, & Popow, 2018;Turner et al., 2012).
Gambling and gaming have been found to share a number of similarities with both activities holding the potential for convergence (Griffiths, 2008b;King, Delfabbro, & Griffiths, 2010). Indeed, multiple similarities have been noted at the structural (e.g., variable reinforcement schedules), esthetic (e.g., exciting and stimulating sounds and light effects) and motivational (e.g., escapism, socializing) levels (Hilgard, Engelhardt, & Bartholow, 2013;King, Gainsbury, Delfabbro, Hing, & Arabanel, 2015). The distinction between gambling and gaming has been muddled even further with the integration of microtransactions and "loot boxes" in many mobile and console games, allowing gamers to spend money for a chance at acquiring random virtual items of differing value or benefit (Griffiths, 2018;Li, Mills, & Nower, 2019;Richard, 2018;Zendle, Meyer, & Over, 2019). However, some differences between both behaviors are also present. For one, video games do not have any formally legislated age restrictions, whereas gambling is legally restricted to adults in most jurisdictions. Additionally, video games are most often played for points and/or status, with skill determining one's performance, whereas gambling can be engaged in for money with the outcome being predominantly random (Griffiths, 2005). Lastly, although variable reinforcement schedules in gambling and gaming can make these activities more addictive, some video games do not utilize immediate reinforcement, with more delayed rewards being presented to the player after long periods of strategic and goal-directed engagement (James & Tunney, 2017).
Various psychosocial risk factors for the development of problematic engagement in both gambling and gaming have been identified. However, a significantly greater amount of research has investigated PG as the growth of studies investigating PVG largely begun in the 2000s with the rise of online gaming (Griffiths, Kuss, & King, 2012). Recent literature reviews have indicated that males (Brezing, Derevensky, & Potenza, 2010;Dowling et al., 2017) and younger individuals (Derevensky, 2019;Johansson, Grant, Kim, Odlaug, & Gotestam, 2009) are at an increased risk of PG and PVG. Moreover, high sensation seeking (Dowling et al., 2017;Shead, Derevensky, & Gupta, 2010), emotion-focused coping styles (i.e., suppressive and reactive; Johansson et al., 2009;, depressive symptoms (Johansson et al., 2009;, attention problems (Shead et al., 2010;Sugaya, Shirasaka, Takahashi, & Kanda, 2019), delinquency (Johansson et al., 2009;Shead et al., 2010), and conduct problems (Dowling et al., 2017;Sugaya et al., 2019) have been identified as risk factors for both PG and PVG. As numerous risk factors have been identified, there is a serious need to understand which of these are of critical importance when investigating the development and maintenance of these problem behaviors.
Theoretical models for the development of substance use disorders and non-substance addictive behaviors can provide a rationale to specify which risk factors are predominant in the development of PG and PVG. The potential generalizability of these models is based on research demonstrating that there are etiological, neurobiological, clinical, and phenomenological similarities between substance and non-substance addictions (Brezing, Derevensky, & Potenza, 2010;Potenza, 2014;Yakovenko & Hodgins, 2018). Based on a developmental psychopathology framework, various pathways have been suggested to explain the development of substance use disorders (SUDs) including the externalizing pathway, internalizing pathway, and combined pathway. The externalizing pathway suggests that early externalizing problems (e.g., conduct problems) and behavioral disinhibition predict later SUDs (Zucker, 1994;Zucker, Heitzeg, & Nigg, 2011). The internalizing pathway proposes that early inhibited temperament, internalizing symptoms (e.g., depression) and difficulties with emotional coping predict later SUDs (Hussong, Jones, Stein, Baucom, & Boeding, 2011;Trucco, Villafuerte, Hussong, Burmeister, & Zucker, 2018). Lastly, the combined pathway proposes that a combination or interaction of externalizing and internalizing problems leads to the development of SUDs (Englund & Siebenbruner, 2012;Maslowsky, Schulenberg, & Zucker, 2014), which may be explained by the presence of shared mechanisms underlying psychopathology (Angold, Costello, & Erkanli, 1999;Caspi & Moffitt, 2018).
Recently, two of these pathways have been indirectly adapted to explain the development of gaming disorder. Based on case reports, Benarous et al. (2019) identified an "internalized pathway" (involving depressive symptoms during adolescence) and an "externalized pathway" (involving conduct problems during adolescence) towards the development of gaming disorder in young adulthood. Indeed, subtypes of problem gamers have been identified depicting greater aggressive and/or depressive symptoms (Lemmens, Valkenburg, & Gentile, 2015;Myrseth & Notelaers, 2018;Sanders & Williams, 2019;Yu & Cho, 2016), with longitudinal studies identifying the predictive role of greater internalizing and externalizing symptoms for problem gaming (Krossbakken et al., 2018;Liu et al., 2018).
Although these specific developmental pathways have not been empirically or theoretically investigated with regards to PG, Yakovenko and Hodgins (2018) discuss the potential for the SUD literature to act as a model for future research related to gambling disorder. Linking these pathways to what has been theoretically established for PG, these appear to parallel the two subgroups of problem gamblers identified within the Pathways Model (Blaszczynski & Nower, 2002), namely, the antisocial impulsivist (Pathway 3) and emotionally vulnerable (Pathway 2) problem gamblers. Importantly, the presence of these subgroups of problem gamblers has been empirically validated using crosssectional community (Gupta et al., 2013;Nower, Martins, Lin, & Blanco, 2013), clinical (Moon, Lister, Milosevic, & Ledgerwood, 2017;Valleur et al., 2016), and longitudinal data (Allami et al., 2017;Dowd, Keough, Jakobson, Bolton, & Edgerton, 2018;Mader, Christensen, & Williams, 2019). Lastly, as a combined pathway has been identified within the SUD literature, it is possible that comorbid externalizing and internalizing problems may also be related to the development of behavioral addictions. This combined pathway would be consistent with the subgroup of adolescent problem gamblers identified by Gupta et al. (2013) reporting higher levels of both externalizing and internalizing symptoms. This combined pathway presently remains unexplored with regards to PVG.
Given the theoretical and empirical associations between CP, DS and behavioral addictions, a review of the literature investigating the role of these problems in the development of PG and PVG is deemed necessary. Previous reviews have broadly examined the role of various risk and protective factors for PG (Dowling et al., 2017;Johansson et al., 2009;Lorains, Cowlishaw, & Thomas, 2011;Yakovenko & Hodgins, 2018) and PVG (Burleigh, Griffiths, Sumich, Stavropoulos, & Kuss, 2019;Cheng, Cheung, & Wang, 2018;Gonz alez-Bueso et al., 2018;Mihara & Higuchi, 2017). However, these reviews have not investigated both PG and PVG together, with an emphasis on DS and CP. With the inclusion of gaming disorder as the second formally recognized behavioral addiction (WHO, 2019), reviews investigating both PG and PVG are necessary to assess for similarities and differences in the risk factors and mechanisms underlying the development of each problem behavior (Marchica, Mills, Derevensky, & Montreuil, 2019). Furthermore, as adolescents and young adults present with a higher risk for the development of these problem behaviors, a review targeting this demographic is of primary interest. Several reviews have limited their sample to adolescents and young adults, yet these are limited in their broad examination of factors associated with PG (Calado, Alexandre, & Griffiths, 2017) or PVG (Paulus et al., 2018;Sugaya et al., 2019), with no focus on CP and DS. As such, the purpose of the present systematic review is to provide an overview of research identifying the relationship between CP, DS and both PG and PVG among adolescents and young adults.

Study selection
The methodology employed in this review is compliant with the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA; Moher, Liberati, Tetzlaff, & Altman, 2009). Electronic databases including PsychINFO, Medline, Social Work Abstracts, Scopus and Web of Science were searched. Searches in all databases utilized a combination of Medical Subject Headings (MeSH) and multipurpose terms where applicable, searching for the keywords in the title, abstract, keywords, headings and subject headings of articles. The search terms used a combination of keywords and Boolean terms relating to gambling, gaming, CP and DS. Keywords for the searches are presented in Table 1. The search was restricted to articles published from January 1994 to October 2019, to coincide with the publication of the DSM-IV (APA, 1994) which introduced a scientific and empirically-based understanding of pathological gambling (National Research Council, 1999, p. 18). The search strategy was peer-reviewed by a university librarian with experience conducting systematic reviews. The search parameters yielded the following number of results in each database: PsychINFO (296), MEDLINE (945), Social Work Abstracts (22), Scopus (1,623), and Web of Science (915).
Inclusion criteria were developed for the title/abstract screening stage and full text screening stage. Studies were considered eligible at the title/abstract stage if they were: (1) original peer-reviewed publications in English or French; (2) providing an estimate of the presence of CP (i.e., physical or verbal aggression, delinquency, antisocial behavior, externalizing problems) or DS (i.e., low mood, negative affect, anhedonia, internalizing symptoms) in association with either PG or PVG; (3) observational and descriptive studies (e.g., cross-sectional, case-control, longitudinal); (4) reviews if they included the calculation of new data (i.e., metaanalysis). Studies were not eligible at the title/abstract screening stage if they were: (1) validating the development of a psychometric measure/scale; or (2) investigating the impact of a treatment intervention.
Studies were included at the full-text screening stage if: (1) participants were between the ages of 12 and 25 years; (2) the study included a measure specific to problem/disordered gambling or problem/disordered gaming as the dependent variable; and (3) the study included a measure specific to CP or DS as the independent variable. Studies were excluded at the full-text screening stage if they: (1) only included a measure for impulsive behavior, sensation seeking or substance use (and not CP more specifically); (2) only included a measure of emotional problems based on a composite of both anxious and depressive symptoms without isolating the effect of DS; or (3) investigated Internet addiction/problems without isolating the effect of PVG.

Study assessment
A PRISMA flow diagram of the search results is displayed in Fig. 1. A total of 2,549 articles were identified after duplicate records were removed. Rayyan QCRI (Ouzzani, Hammady, Fedorowicz, & Elmagarmid, 2016) was utilized to perform the blind screening of identified articles. To ensure reliable title and abstract screening, approximately 20% (n 5 527) of the titles and abstracts were randomly selected and reviewed by JR and EF. The inter-rater agreement across the reviewers was 95.64%. After the title/ abstract screening, 571 full-text articles were deemed potentially eligible and were retrieved for review. To ensure reliable full-text screening, approximately 20% (n 5 114) of the full-texts were randomly selected and reviewed by JR and EF. The inter-rater agreement across the reviewers was 94.74%. Discrepancies were resolved through group discussion with a third reviewer (CT) as arbiter and inclusion/exclusion criteria were specified or adjusted as necessary. After the full-text screening, 71 articles met the inclusion criteria for the study. Gambling or gaming (gambl* OR gambling OR "problem gambling" OR "disordered gambling" OR "gambling disorder" OR "pathological gambling" OR "video game" OR videogame OR games OR gamer OR "problem* use of video games" OR "Internet gaming disorder" OR "gaming disorder") AND Conduct problems or depressive symptoms (conduct* OR "conduct problems" OR "conduct disorder" OR delinquency OR aggression OR externaliz* OR "externalizing problems" OR "externalizing symptoms" OR "oppositional defiant disorder" OR "antisocial personality disorder" OR "antisocial behavio*r" OR depression OR "major depression" OR "major depressive disorder" OR "major depressive episode" OR dysthymia OR "mood disorder" OR internaliz* OR "internalizing problems" OR "internalizing symptoms")

Sample characteristics
Sample characteristics of selected studies are presented in Tables 2-4. Approximately 59% of the studies were published within the past five years (2014-2019), with the majority of the studies being carried out in Canada (n 5 22), Europe (n 5 22), and the United States (n 5 16). Fortyseven studies examined PG (33 cross-sectional and 14 longitudinal), 23 studies examined PVG (18 cross-sectional and five longitudinal) and one cross-sectional study investigated both PG and PVG. A majority of the studies utilized convenience sampling methods (n 5 49), with others applying random, stratified, or cluster sampling methods. As for the gender of individuals in study samples, 15 studies reported samples that were more than 60% male and seven studies reported samples that were more than 60% female. The most commonly sampled populations included high-school students (n 5 23), adolescents/young adults (n 5 14), and university students (n 5 11).

Measures
Problem gambling (PG) and problem video gaming (PVG). Commonly used measures for PG include: adolescent and adult versions of the South Oaks Gambling Scale (SOGS; Lesieur & Blume, 1987;Winters, Stinchfield, & Fulkerson, 1993)  (n 5 2). Compared to PG, there appeared to be a greater variation in the instruments used to assess PVG, with multiple studies using scales developed specifically for the study in question.

Conduct problems
Problem gambling (PG). A total of 15 studies (11 crosssectional and four longitudinal) were included investigating the relationship between CP and PG (Table 2). Seven crosssectional studies indicated that problem gamblers experienced greater CP compared to those with no gambling problems, with relative risk or odds ratios ranging from 1.01 to 19.6 ( Barnes et al., 2011;Brunelle, Leclerc, Cousineau, Dufour, & Gendron, 2012a;Cheung, 2014;Cook et al., 2015;Hayatbakhsh et al., 2013;Welte et al., 2009;Willoughby et al., 2004). Additionally, Brunelle and colleagues (2012b) reported that CP were related to an increased severity of PG in both Internet and non-Internet gamblers. Terrone et al. (2018) investigated the relationship between CP and PG while measuring the moderating role of attachment style. The authors reported that although CP were associated with PG among those with a dismissing-detached attachment style, this was not the case among those with a fearfulavoidant attachment style. The remaining two studies reported non-significant associations between CP and PG (Pace et al., 2013;Widinghoff et al., 2019). Evidence from cross-sectional studies indicate strong evidence for a positive association between CP and PG. The two cross-sectional studies that did not report significant associations between CP and PG were similar in that they included a relatively small sample size of males. In their study, Pace and colleagues (2013) report that at-risk (M 5 1.09, SD 5 0.54) or pathological gamblers (M 5 1.19, SD 5 0.68), did not differ from non-gamblers (M 5 1.11, SD 5 0.55) with regards to CP. However, CP did differentiate between at-risk and pathological gamblers. Given the study's  Correlation between delinquency and PG was significant (r 5 0.24, P < 0.001). Violent and non-violent delinquent behaviors were more common in PG than non-PG, with ORs ranging from 3.4 to 19.6 depending on the delinquent act. Overall delinquency scores indicated 11.35 times (P < 0.001) higher likelihood of PG. Stratified (region and school type), two-stage (school, class) cluster sampling 53% female A multivariate logistic regression indicated that higher overall delinquency resulted in youth being 5.9 times (P < 0.001) more likely to meet the criteria for PG compared to less delinquent youth when controlling for hazardous drinking, cannabis dependency, suicide attempt(s) and psychological distress.  A greater proportion of problem gamblers (65%) were arrested before the age of 23 compared to social (38%) and non-gamblers (24%). PG was significantly associated with the hazard of first arrest by age 23 in both the unadjusted (HR 5 3.6, P < 0.001) and adjusted (covarying for gambling status, race, household structure, lunch status, intervention status, theft/property damage, illegal drug use; AHR 5 1.6, P 5 0.05) models The group of at-risk and pathological gamblers compared to nongamblers did not endorse higher levels of CP (P > 0.05). Convenience sampling 100% male In the discriminant function analysis, higher CP was one of the variables that best differentiated at-risk gamblers from pathological gamblers (pathological gamblers having slightly more CP) but did not differentiate between non-gamblers and at-risk gamblers.   Correlations between CP and PG were significant ranging from r 5 0.16-0.18 (P < 0.001). Results from the confirmatory factor analysis indicated a three-factor model with a delinquency factor including major delinquency (b 5 0.50, P < 0.001), minor delinquency (b 5 0.57, P < 0.001), and gambling (b 5 0.30, P < 0.001). This factor was significantly correlated with the aggression factor (r 5 0.63). Lastly, there was a consistent co-occurrence of CP and PG across levels of severity (risk ratios ranging between 1.01 and 3.45, all P < 0.001).
South Korea

Cross-sectional study
First year middle-school students N 5 402 IGUESS BPAQ Correlation analyses indicated a positive correlation between CP and PVG (r 5 0.32, P < 0.001). A mediation model was created with father-adolescent communication as a mediating variable between CP and PVG. CP were directly related to PVG (b 5 0.29, P < 0.001), with a significant partial indirect effect through poorer father-adolescent communication (b 5 0.19, P < 0.001). The total effect of the model was significant (b 5 0.42, P < 0.001). The cluster analysis indicated three clusters in the data; 1) comorbid-PVG, 2) social-PVG and 3) non-PVG. The comorbid-PVG cluster, had significantly higher levels of CP compared to the non-PVG group (P < 0.001).         DS and PVG were positively correlated (r 5 0.17, P < 0.01). Those with PVG endorsed greater DS than those with no-PVG (22.6% vs 6.5%, P < 0.001). In the linear regression model, DS were a significant predictor of PVG (b 5 0.18, P < 0.01) when controlling for occupation, education level, age, gaming frequency, health, exercise, life satisfaction, and preference for online interaction.  Analyses were conducted separately by gender. In males, DS were associated with an increase in PVG (d 5 0.91, P < 0.001). In females, DS associated with an increase in PVG (d 5 1.23, P < 0.001).  Correlation analyses indicated significant correlations between CP and PG (r 5 0.08-0.16, P < 0.01) and DS and PG at 16 and 23 years (r 5 0.07-0.09, P < 0.01).  Results from the latent class analyses identified 5 classes. These classes support the groups identified within the Pathways Model (Blaszczynski & Nower, 2002), in addition to a DS only class (27%) and a combined (DS/CP) (10%) class.

Canada (Ontario)
Cross-sectional study High-school students N 5 2,336 DSM-IV-MR-J CP & DS: Conners-Wells Adolescent Self-Report Scale CP were the largest clinical problem for probable PG, with 55% of the latter reporting clinical levels of CP, which was greater than the CP reported by non-gamblers and social gamblers (P < 0.001). Similar findings were reported for DS, with 27.4% of probable PG reporting such problems and this being greater than the DS reported by non-gamblers and social gamblers (P < 0.001). Convenience sampling 42% male In the regression model controlling for family problems, anger control problems, hyperactivity, and inattention, CP was significant in predicting at-risk/probable PG (b 5 0.083, Exp(b) 5 1.087, P < 0.001). However, DS was nonsignificant. In the sample, 34% never gambled, 57% were social/nonproblem gamblers, 8% (n 5 8) were at-risk and 1% (n 5 1) met the criteria for pathological gambling.
(continued) Five groups were identified from the discriminant function analyses: 1) non-gambler; 2) non-problem gambler; 3) atrisk gambler; 4) problem gambler and; 5) pathological gamblers. CP were a significant predictor in the linear progression from least to most PG, DS were not a significant predictor.

Convenience sample
Gender NR DS: CES-D Pathological gamblers reported significantly more CP (M 5 1.36) and more DS (M 5 0.88) than did individuals in the (continued)  Individuals with PG were more likely to report past year DS in comparison to low-risk (OR 5 4.15, P < 0.001) and atrisk gamblers (OR 5 3.95, P < 0.001). Individuals with PG were also more likely to report serious fights (OR 5 6.48, P < 0.001; OR 5 6.45, P < 0.001) and carrying a weapon to school (OR 5 3.40, P < 0.001; OR 5 2.89, P < 0.001) compared to low-and at-risk gamblers.  In the unrestricted path model, DS were reciprocally related to PVG (as both an antecedent [b 5 0.11-0.12, P < 0.01]; and a consequence [b 5 0.12-0.13, P < 0.01]). However, physical aggression was only an antecedent to PVG (b 5 0.08, P < 0.05). Based on a typology of gamers (engaged, problem, addicted), physical (OR 5 1.10-1.19, P < 0.01) and verbal aggression (OR 5 1.11, P < 0.01) and DS (OR 5 1.11, P < 0.01) were antecedents of PVG over a 1-year, but not a 2-year interval. Correlations indicate a positive relationship between PVG and CP (r 5 0.30, P < 0.01). Adolescents in the PVG group reported significantly greater levels of CP (males, M 5 24.5; females, M 5 25.9) compared to non-problematic and nongamers (M scores for males and females range between 10.9 and 11.5; h 2 5 0.033, P < 0.001).  CP: BPAQ Analyses indicated that the PVG group reported a significantly higher mean score of DS (M 5 14.21) compared to the non-gamer (NG; M 5 12.0), at-risk gamers (M 5 11.76), and regular gamer (RG; M 5 11.06) groups. Based on the cut-off score for DS, 15.1% of PVG had DS, compared to 5.1% of NG, 2.5% of at-risk gamers and 2.8% of RG. Further, analyses indicated that the PVG group reported the highest mean score in CP (M 5 16.18), Univariate analyses indicate that both PG (P < 0.01) and PVG (P < 0.001) reported more CP, but not more DS compared to non-problem gamblers (P 5 0.71) and nonproblem gamers (P 5 0.10). Multivariate analyses indicate that PVG reported more CP (OR 5 1.65, 95% CI [1.01-2.69]) but not more DS than non-problem gamers. PG reported no significant differences in either CP or DS. small sample size, it is possible that the non-significant difference was related to the lack of statistical power within the analyses. As for Widinghoff et al. (2019), they investigated violent offenders in prison where rates of conduct disorder in the overall sample was of 79.2%. Due to the elevated rates of conduct disorder in the non-PG (77.4%) and PG (88.4%) groups, it is possible that there was a ceiling effect associated with abnormally elevated levels of CP. Two out of the four longitudinal studies reported significant relationships between CP and PG. Martins et al. (2013) reported that boys with chronically high CP throughout adolescence were more likely to be at-risk or problem gamblers by early adulthood. Martins et al. (2014) expanded on these findings by noting that problem gamblers in early adulthood were more likely to have been arrested before the age of 23 compared to social or nongamblers. In contrast to these results, two studies of a duration of 2-and 7-years, respectively, reported that CP at age 16 did not predict PG at age 17 (Vitaro et al., 2001) or 23 (Wanner et al., 2009. All four studies sampled predominantly male youth from disadvantaged neighborhoods, with some overlap in the included samples (i.e., Vitaro et al., 2001;Wanner et al., 2009). As there were differences in the times at which CP was measured between the studies and differences in the types of CP measured, it is possible that the presence of CP (primarily aggression) in early adolescence , as opposed to CP (primarily delinquency) in later adolescence (Vitaro et al., 2001;Wanner et al., 2009), is of greater importance when predicting PG in young adulthood.
Problem video gaming (PVG). A total of five studies (four cross-sectional and one longitudinal) investigated the relationship between CP and PVG ( Table 2). All four crosssectional studies reported significant associations, with three studies finding a positive association between CP and PVG (Kim et al., 2018;Tejeiro et al., 2012;Wartberg et al., 2017), and one study finding that those with a history of CP were less likely to be problem gamers (Ong et al., 2016). Differing results may have been reported in the study by Ong and colleagues (2016) because they investigated a relatively small sample of adolescents presenting at an addiction treatment center in Singapore. Moreover, the authors measured CP dichotomously which does not account for the severity of the behaviors when compared to the other three studies that measured CP continuously.
Only one longitudinal study investigated the prospective relationship between CP and PVG. This study was an extension of Wartberg and colleagues (2017) and they reported that CP at baseline did not predict PVG one year later when accounting for other psychosocial predictors (Wartberg et al., 2019). Overall, there is a paucity of research investigating the association between CP and PVG. Although cross-sectional results are encouraging, longitudinal findings do not confirm the presence of a prospective relationship between CP and PVG.

Depressive symptoms
Problem gambling (PG). A total of 18 studies (12 crosssectional and six longitudinal) investigated the relationship between DS and PG (Table 3). Ten cross-sectional studies reported significant positive associations between DS and PG. Notably, greater DS were reported among problem gamblers compared to non-problem gamblers (Dowd et al. 2018;Ellenbogen et al., 2007;Martin et al., 2014;Nower et al. 2004;Sanscartier et al., 2018;Stuhldreher et al., 2007;Wohl et al., 2008). Moreover, in linear and logistic regression analyses, DS were associated with greater PG severity after controlling for various psychosocial and demographic variables (Cosenza et al., 2019;Molde et al., 2009;Nigro et al., 2017).
The remaining two cross-sectional studies reported nonsignificant associations between DS and PG (Delfabbro and Grabosky, 2006;Pascual-Leone et al., 2011). Pascual-Leone and colleagues (2011) reported a non-significant correlation in their sample which may have been a result of the study's small sample size (N 5 200) of university students, with low overall levels of PG (15 reported at-risk or probable pathological gamblers) and DS (23 reported moderate to severe depression). Further, although Delfabbro & Grabosky (2006) reported a moderate effect size of DS on the presence of PG (d 5 0.49), this effect became non-significant when controlling for other psychosocial factors including self-esteem and social alienation (correlation coefficients not reported in the study). Overall, based on the cross-sectional studies, there appears to be good evidence for a positive association between DS and PG.
In the six longitudinal studies, two report significant relationships whereby DS predicted PG one-month (Bilevicius et al., 2018), and six-years later (Dussault et al., 2016). Although the remaining four studies indicated crosssectional associations between DS and PG (Afifi et al., 2016;Chinneck et al., 2016;Edgerton et al., 2015Edgerton et al., , 2018, these relationships were non-significant in the prospective analyses. It is important to note that all four of these studies utilized the same cohort (Manitoba Longitudinal Study of Young Adults) over time periods ranging from one to five years. Furthermore, Bilevicius and colleagues (2018) only had a one-month period between both time points which brings into question whether these results would be maintained over longer periods of time. Lastly, as Dussault and colleagues (2016) focused solely on males living in economically disadvantaged areas, it is possible that these individuals present with different psychosocial developmental trajectories compared to young adults in the general population. Overall, longitudinal evidence for the relationship between DS and PG is mixed, with a trend towards DS being a poor predictor of PG.
Problem video gaming (PVG). A total of 10 studies (seven cross-sectional and three longitudinal) investigated the relationship between DS and PVG (Table 3). To begin, two studies reported that problem gamers endorsed greater DS compared to non-problem gamers (Givron et al., 2018;Van Rooij et al., 2014). Additionally, three studies indicated significant positive associations between DS and PVG when controlling for demographic characteristics and other psychosocial factors (Bonnaire & Baptista, 2019;M€ annikk€ o et al., 2015;Vadlin et al., 2016). As for structural equation models, Li and colleagues (2011) report that although the direct path between DS and PVG was non-significant, an indirect path existed via escapism and actual-ideal selfdiscrepancies. However, Kircaburun and colleagues (2019) identified that DS were a non-significant mediator in the relationship between emotional intelligence and PVG.
All three longitudinal studies reported significant relationships between DS and PVG. Investigating the crosssectional associations between DS and PVG at each time point, Dang and colleagues (2019) report these associations were significant at baseline and one-year later. As for the prospective results, Guillot and colleagues (2016) report that anhedonia predicted greater levels of PVG one year later (OR 5 1.33). Similarly, Liu et al. (2018) report that greater DS at baseline were associated with greater PVG one, two, three and four years later. Given these consistent positive associations in both the cross-sectional and longitudinal research, there appear to be good evidence for the concurrent and temporal associations between DS and PVG.

Conduct problems and depressive symptoms
Problem gambling (PG). A total of 14 studies (10 crosssectional and four longitudinal) investigated the relationship between both CP, DS, and PG (Table 4). Three crosssectional studies reported that at-risk and problem gamblers endorsed greater DS and CP compared to low and no risk gamblers (Giralt et al., 2018;Potenza et al., 2011;Yip et al., 2011). Furthermore, in the two studies utilizing latent class analyses, problem gamblers could be separated based on the presence of greater CP or greater DS (Gupta et al., 2013;Kong et al., 2014). Moreover, Gupta et al. (2013) also identified a class of problem gamblers with higher levels of both CP and DS.
Alternatively, three cross-sectional studies reported that although the association between CP and PG was significant, the association between DS and PG was not. Although Hardoon et al. (2004) reported that problem gamblers endorsed greater levels of CP and DS, only CP were significantly associated with at-risk/probable PG. In the other two studies, problem gamblers were more likely to endorse greater severity of CP but not DS compared to nonproblem gamblers (Langhinrichsen-Rohling et al., 2004;Petry & Tawfik, 2001).
As for the remaining studies, Tackett et al. (2017) investigated these relationships by gender and reported that although both DS and CP were correlated with PG among women, only CP were significant for men. Finally, Kaminer et al. (2002) reported no significant association between either DS and PG, and CP and PG. It is important to note that the study included a small number (N 5 97) of adolescents diagnosed with psychoactive substance use disorders, where only nine individuals were identified as being at-risk/pathological gamblers. Overall, results from the cross-sectional studies indicated that both CP and DS were generally positively associated with PG, with other studies indicating that only CP were associated with PG. None of the cross-sectional studies indicated that DS were solely associated with PG.
In the four longitudinal studies, two studies reported significant relationships between both DS, CP, and PG. Allami et al. (2017) identified two classes of problem gamblers with higher levels of CP and DS, respectively, and that membership within these classes at age 12 was a significant predictor of PG at age 23. Additionally, Sagoe et al. (2017) report that at-risk and PG classes had greater concurrent levels of CP and DS from age 17 to 19. In contrast to these findings, although Allami, Vitaro, Brendgen, Carbonneau, and Tremblay (2018) utilized the same samples reported in their 2017 study, they identified a third comorbid (high CP and DS) class of adolescents. However, only the high CP and comorbid classes had greater levels of PG at age 16 and 23. Finally, in a 6-year longitudinal study, no significant overall differences in DS and CP were noted across different levels of gambling risk across time. However, sex-dependent effects were identified whereby greater levels of parental-reported CP predicted PG among females, and lower levels of parental-reported CP predicted PG among males (Y€ ucel et al., 2015). Overall, longitudinal findings appear to have established a greater consistency regarding the predictive role of both CP and DS for later PG, followed by CP.
One longitudinal study investigated the predictive role of both CP and DS on later PVG. In this study, Krossbakken et al. (2018) reported that both DS (b 5 0.11-0.12) and CP (b 5 0.08) predicted PVG. Moreover, both CP (OR 5 1.10-1.11) and DS (OR 5 1.11) predicted membership to the group of problem gamers one year, but not two years later. Overall, all seven cross-sectional studies and the one longitudinal study reported significant associations between both DS, CP and PVG. Although there is strong cross-sectional evidence, with results indicating that the association may be stronger for DS compared to CP, the paucity of longitudinal research limits the extent to which conclusions can be drawn regarding the predictive role of CP and DS on PVG.
Problem gambling (PG) and problem video gaming (PVG). One cross-sectional study measured both PG and PVG, in addition to CP and DS (Table 4). In a sample of German students (Walther et al., 2012), multivariate analyses controlling for demographic characteristics and parental monitoring indicated that problem gamers reported greater CP, but not greater DS compared to non-problem gamers. However, problem gamblers did not report greater CP or DS in the multivariate models, even if those with PG reported greater CP in the univariate model. It is noteworthy that in this study, only a small proportion of individuals were identified as problem or probable pathological gamblers (1.3%).

DISCUSSION
The aim of this systematic review was to provide an overview of research identifying the relationship between CP, DS and both PG and PVG among adolescents and young adults. Overall, the results from these studies indicate important distinctions in the role of CP and DS as risk factors for PG and PVG. Present findings are consistent with the wider literature identifying both CP and DS as significantly associated with PG (Dowling et al., 2017;Johansson et al., 2009;Shead et al., 2010) and PVG (Brezing et al., 2010;Sugaya et al., 2019). What is novel in the present review is the identification of the extent to which these claims can be made among adolescents and young adults, with an emphasis on the quantity and methodological quality of studies and the differences between the concurrent and prospective associations. Based on theoretical models for the development of addictive behaviors, there appears to be greater evidence for a combined pathway (Englund & Siebenbruner, 2012;Maslowsky et al., 2014) for the development of both PG and PVG, an externalizing pathway (Zucker, 1994;Zucker et al., 2011) for the development of PG, and an internalizing pathway (Hussong et al., 2011;Trucco et al., 2018) for the development of PVG. These results suggest that although both CP and DS are generally associated with PG and PVG, they may exert different effects on the development of these problem behaviors.
The difference in the extent to which CP and DS are related to PG and PVG warrants further discussion. To begin, CP were identified as a greater risk factor for PG when compared to PVG. In the broader literature, CP have been frequently associated with PG under a general pattern of co-occurring problem behaviors as a result of shared etiological factors (Blaszczynski & Nower, 2002;Jessor & Jessor, 1977;Welte, Barnes, & Hoffman, 2004;Willoughby, Chalmers, and Busseri, 2004). For instance, risk factors for antisocial behaviors and conduct problems include impulsivity and behavioral disinhibition, which may explain why these individuals are at a greater risk for later PG. As impulsivity has been identified as increasing the risk for both adolescent PG (Secades-Villa, Mart ınez-Loredo, Grande-Gosende, & Fern andez-Hermida, 2016) and conduct problems (Ahmad & Hinshaw, 2017;Olson, Schilling, & Bates, 1999), it may be an important factor in the etiology of both behaviors. Overall, these predispositions would be consistent with what has been identified for the externalizing pathway (Zucker, 1994;Zucker et al., 2011).
As for gaming, PVG has not typically been associated with CP, nor included under the classic umbrella of the problem behaviors (Welte, Barnes, & Hoffman, 2004;Willoughby, Chalmers, and Busseri 2004). Indeed, there are noteworthy differences between gambling and gaming which may differentiate the two including the legality of the activity for adolescents and the close connection of youth gambling with other delinquent acts (Burleigh et al., 2019;Welte, Barnes, & Hoffman, 2004;Willoughby, Chalmers, & Busseri, 2004). An important point of distinction here may be that video game playing in youth is not as strongly associated with delinquency when compared to gambling. Additionally, all five included studies investigating PVG and CP were comprised primarily of samples of youth in early adolescence, with aggressive behaviors being more prominent in childhood and early adolescence and delinquent behaviors typically peaking in late adolescence (Fonagy & Luyten, 2018;Hawkins et al., 2002). As such, the age of the samples could potentially explain why evidence for the association between delinquency and PVG is mixed. Nevertheless, it is possible that specific conduct problems such as aggression and rule-breaking pose a higher risk for PVG compared to others including violent or delinquent behaviors. A potential common factor underlying aggression, rule-breaking and problem gaming could be impulsivity (specifically, impulsive decision making and urgency), which has been found to be more prominent among problem gamers (Billieux et al., , 2011Tian et al., 2018). Given the paucity of research in this domain, further research is necessary to elucidate the differences between specific conduct problems and their predictive value for PVG. DS appear to be more consistently associated with PVG in both cross-sectional and longitudinal studies. For one, it is possible that the difficulties with emotional coping and emotional dysregulation experienced by those with elevated DS is related to the development of PVG. As the included studies investigating DS and PVG were comprised of samples ranging from early adolescence to young adulthood, it would appear as though these associations are present across these developmental periods. These predispositions and risk factors would be consistent with the internalizing pathway (Hussong et al., 2011;Trucco et al., 2018). Moreover, symptoms of PVG as outlined in the DSM-5 (APA, 2013) and ICD-11 (WHO, 2019) include a loss of interest in previous hobbies/activities, negative emotions (e.g., irritability, sadness) when gaming it taken away, and the use of games to relieve a negative mood (e.g., guilt). These symptoms have important overlaps with those of depression, which include anhedonia, depressed mood, and feelings of worthlessness or inappropriate guilt (APA, 2013). As such, it is possible that these two disorders share symptomatology in a manner that creates a downward spiral of DS and PVG, leading to a significant deterioration of psychological wellbeing over time. However, evidence for these temporal relationships are limited to samples of university students and emerging adults, with additional research being necessary to establish these links in early adolescents. Although similar claims could be made for PG and DS, temporal interrelationships remain inconclusive with stronger evidence for their concurrent associations. Given that gambling is an age-restricted activity in most jurisdictions, it is possible that these prospective associations become clearer later in adulthood.
Based on the included studies, the presence of both CP and DS appear to increase the risk for the development of PG and PVG. Although CP and DS are etiologically heterogeneous (Angold et al., 1999), this would be consistent with the combined pathway (Englund & Siebenbruner, 2012;Maslowsky et al., 2014). A potential hypothesized mechanism underlying this comorbid association could be the role of poor impulse control and emotion dysregulation (Angold et al., 1999;Caspi & Moffitt, 2018). Of note, poor impulse control and emotion dysregulation could explain the shared variance of internalizing (e.g., depression) and externalizing (e.g., conduct) problems, their continuity over time, and the later emergence of addictive behaviors due to poor behavioral inhibition and continued engagement in the behavior as a maladaptive learned coping strategy. Moreover, it is also possible that the predisposition towards poor impulse control or emotion dysregulation is related to gender, with Tackett et al. (2017) reporting that PG among young adult males could be related to risk-taking and impulsivity (as represented by CP) and PG among young adult females being related to affective dysregulation (as represented by DS). However, heightened CP among females may also be indicative of maladjustment (Crick, 1997), which is consistent with the findings by Y€ ucel et al. (2015) identifying that higher levels of aggressive behavior in early adolescent females predicted PG in late adolescence. Overall, further research investigating the effect of CP and DS at different time-points across adolescence and young adulthood, while isolating the effects for males and females will be essential to understand whether the presence of these symptoms at different times represents a greater or lesser risk for the development of PG and PVG.
A major limitation of the included research studies is the shortage of longitudinal research investigating PG and PVG. Although 14 studies were included investigating the predictive role of CP and/or DS on later PG, only five studies were included with regards to PVG. As such, additional studies are necessary to draw clear conclusions regarding the predictive role of both of these risk factors for later PVG. Furthermore, there is a pressing need for greater consistency in the instruments used to measure PVG in order to ensure that different researchers are measuring the same latent construct. Additionally, there is a need to investigate the interaction of these two variables in the way they predict PG or PVG. Understanding the interaction of CP and DS in predicting PG and PVG will lead to important insights regarding the complexity of these symptoms with the potential of identifying youth at the highest risk for these problem behaviors and more concrete evidence for the combined pathway. Moreover, only one study investigated both PG and PVG among adolescents and young adults (Walther et al., 2012). Further research is necessary to clarify the developmental pathways of behavioral addictions and whether youth who report problems with one behavior are at a greater risk of experiencing problems with another at the same or a later time. Although gambling and gaming disorder are the only two formally recognized behavioral addictions (APA, 2013; WHO, 2019), other potential behavioral addictions such as problematic use of the Internet, sex, shopping, tanning, and exercising (Grant, Potenza, Weinstein, & Gorelick, 2010;Petry, Zajac, & Ginley, 2018) could be considered in relation to the risk factors examined in this review in addition to their potential cooccurrence with PG and PVG.

Limitations
Although the present review identified and clarified the role of CP and DS on the development of PG and PVG, it is subject to a number of limitations. First, it is possible that some articles were missed in the systematic search due to relevant terms (i.e., keywords for CP and DS) not being included in the areas searched by the MeSH and multipurpose terms. Although the present study sought to identify articles with CP and DS as independent variables, it is possible that some published articles did not mention these terms in the title, abstract, keywords, headings and/or subject headings, although they were included in the study. As such, certain articles may have been omitted although they could have reported on the associations between the variables of interest. Second, the methodology used in the present review was primarily descriptive with the aim of investigating a breadth of literature. As such, no statistical conclusions can be drawn from the results. Third, the review was limited to English and French peer-reviewed journal publications identified on the five selected databases. Given these criteria, the authors may have omitted studies from other countries that were unavailable through the selected databases. Fourth, although clear inclusion and exclusion criteria and a high inter-rater reliability was established, the review, screening, and selection process is subjective and prone to certain biases. Fifth, a diversity of instruments measuring the constructs of interest (i.e., CP, DS, PG and PVG) were utilized which may have resulted in the measurement of slightly different constructs between studies. Finally, this review focused on adolescents and young adults and did not include children or older adults. Future reviews should aim to investigate the relative role of CP and DS in predicting PG and PVG across the lifespan.

Conclusions
While research in the domain of behavioral addictions is still in its early stages, the results of this review provide preliminary evidence regarding the role of CP and DS as risk factors for PG and PVG. Additionally, this review presents a novel way of investigating the development of PG and PVG, by drawing from a theoretical framework informed by the SUD literature and applying it to non-substance addictive behaviors. Presently, it appears as though there is significant evidence suggesting the importance of a combined pathway, including the presence of both CP and DS, in the development of PG and PVG. However, there also appears to be some evidence for an externalizing pathway for PG, and evidence for an internalizing pathway for PVG. Given the potential for adolescents and young adults to experience early CP or DS, prevention and intervention efforts should focus on intervening in an integrative manner in order to address multiple, potentially interacting problems simultaneously. Authors' contribution: JR, SB, JD and CT designed the study and wrote the protocol. JR conducted the literature search and JR and EF selected the included articles and extracted the data. JR wrote the first draft of the manuscript. All authors reviewed the literature search, data extraction and contributed to the manuscript. All authors contributed to and have approved the final version of the manuscript.

Conflict of interest:
The authors declare no conflict of interest.