Introduction
There is substantial comorbidity between internalizing and externalizing problems across childhood and adolescence (Murray et al.,
2016). Understanding the mechanisms of their relations within individuals over development is essential for identifying key intervention targets (Masten & Cicchetti,
2010) and adolescence is a period of heightened risk for the emergence or escalation of both externalizing (Barbot & Hunter,
2012) and internalizing problems (Rapee et al.,
2019). This study, thus, evaluated the developmental associations between internalizing and an important form of externalizing, namely aggression, in adolescence and examined two candidate mediators of their links: teacher and peer relationships. An autoregressive latent trajectory model with structured residuals (ALT-SR) was employed to overcome a major limitation of the cross-lagged panel models traditionally used in this research area, namely, their conflation of within- and between-person effects.
In developmental approaches to comorbidity, the pathways linking externalizing and internalizing problems have been conceptualized in terms of developmental cascade models. These models suggest that links between domains of psychosocial functioning can emerge through problems in one domain having a causal effect on another (Masten & Cicchetti,
2010). Within this framework, the “dual failure model” proposed by Capaldi (
1992) holds that externalizing problems lead to failures in the academic and social domains resulting in negative self-appraisals and low self-esteem and, in turn, to an increased risk of anxiety and depression. On the other hand, the “acting out model” proposed by Carlson and Cantwell (
1980) holds that children and adolescents who experience anxiety and depression, may “act out” to express their distress; this may alienate them from prosocial friends and lead to conflict at home, which in turn escalates their externalizing behaviors. A large body of longitudinal research has found at least partial support for the dual failure model in both childhood and adolescence (e.g., Blain-Arcaro & Vaillancourt,
2017) and there is some evidence for cascades in the opposite direction, in line with the acting out model (e.g., Yu et al.,
2018).
Peer problems such as rejection and victimization alongside academic problems have been the most commonly tested internalizing-externalizing developmental cascade mediators; however, they have not been found to fully account for the links between these two domains (e.g., van Lier et al.,
2012). Indeed, there may be many further intermediaries that are responsible for the linkages between externalizing and internalizing problems. In the relationships domain, for example, peer relations may be especially significant during adolescence, owing to a heightened importance of peers in this period (Steinberg & Monahan,
2007); however, they are not the only relationships in adolescence that are likely to both be impacted by and impact internalizing problems and externalizing problems. Parental, teacher, and intimate partner relationships, in particular, are also likely to be important. Regarding parental relationships, one previous study examined the role of maternal dissatisfaction in mediating the developmental relations between externalizing and internalizing problems, alongside peer (bullying victimization), and academic problems (Wertz et al.,
2015) and found it to be a significant mediator of a cascade from externalizing problems to internalizing problems. That study, however, only spanned the developmental period from age 5 to 12 and therefore only covered early adolescence. Further research is needed to examine the roles of significant relationships beyond peers in the longitudinal links between externalizing and internalizing problems across adolescence.
Based on transactional theory, teacher relationships are a strong candidate for an additional relationship-based mediator of internalizing-externalizing problem cascades in adolescence. Transactional theory holds that student socioemotional problems are reciprocally related to student-teacher relationships such that problems like externalizing behavior evoke negative reactions from teachers and undermine the formation of warm, supportive teacher-student relationships. According to attachment theory, warm and supportive bonds between youth and significant adults contributes to positive developmental outcomes and student-teacher relationships lacking these qualities have been proposed, by implication, to increase the risk of internalizing and externalizing problems (Pakarinen et al.,
2018). Longitudinal evidence supports the contention that qualities of teacher relationships are reciprocally related to adolescent socioemotional problems. One recent study, for example, used a cross-lagged panel modeling approach to examine the developmental relations between teacher conflict and externalizing problems (Pakarinen et al.,
2018). They found that externalizing problems in grade 4 were related to greater teacher conflict; however, there was no evidence for an effect of teacher conflict on the escalation of externalizing problems. Another recent study using a similar approach found that a good teacher relationship at age 15; characterized by a student feeling fairly treated by their teacher, trusting their teacher, and perceiving that their teacher makes sure there is no violence between students, was related to lower delinquency levels at age 16 (Theimann,
2016). However, there was no such effect across the age 13 to 14 or age 14 to 15 lags. The same study found a significant effect of a bad teacher relationship at age 13, characterized by a student feeling that teachers do not care about their problems and that the teacher tends to look away when it comes to severe fights between students, on delinquency at 14. There was no such effect at the age 14 to 15 or age 15 to 16 lag and no significant effect of delinquency on bad student-teacher relationships. Finally, a study using data from the current sample used a propensity score analysis approach to account for potential confounding and found that children who reported a more positive relationship with their teacher (characterized by getting along well with their teacher, feeling helped by their teacher, and feeling fairly treated by their teacher) compared to their matched pairs at age 10/11 showed less aggression at ages 11, 13, and 15 (Obsuth et al.,
2017). Few studies have addressed the role of teacher relationships in internalizing problems in adolescence and evidence is somewhat mixed. One cross-lagged panel study found evidence consistent with the stress-buffer model, reporting that emotional support from teachers benefitted adolescents with average or high levels of stressful life events; however, those with low levels of stressful life events actually showed later increased depressive symptoms (Pössel et al.,
2013). Another study of similar design; however, found only concurrent (and not cross-lagged) relations between teacher-student closeness and conflict and internalizing problems in adolescence (Pakarinen et al.,
2018). Taken together, the longitudinal evidence suggests that externalizing problems can lead to poorer teacher relationships and that poorer teacher relationships are a risk factor for both externalizing and potentially also internalizing problems in adolescence. This points to teacher relationships as a potential mechanism through which internalizing-externalizing developmental cascades develop and progress throughout adolescence, in addition to peer problems.
In addition to the historically narrow focus on peer and academic problems as cascade mediators, a major issue in externalizing-internalizing cascade research concerns the potential mis-match between developmental cascade models and their statistical operationalization. Much of the strongest evidence for externalizing-internalizing cascade models to date comes from cross-lagged panel models fit to longitudinal data on internalizing, externalizing, and candidate mediators of their association. However, the parameters of the cross-lagged model represent aggregated between- and within- person effects, whereas developmental cascade models of externalizing and internalizing arguably refer to within-person processes (Curran et al.,
2014). As such, accurate tests of externalizing-internalizing cascade hypotheses require statistical models that can separate within-person effects from between-person effects. The ALT-SR model described by Curran et al. (
2014) provides a method of doing this. By fitting a cross-lagged structure to the residuals of a parallel process model (a latent growth curve model with multiple phenotypes with correlated intercepts), the ALT-SR partials out between-person variance, leaving cross-lagged parameters that better capture within-person processes. A similar disaggregation can also be achieved through a random-intercepts cross-lagged panel model (RI-CLPM; Hamaker et al.,
2015). Only a handful of studies have, however, used a statistical design such as an ALT-SR or RI-CLPM that appropriately disaggregates between- and within-person effects and can, thus, provide unambiguous estimates of the developmental links between internalizing and externalizing problems (e.g., Oh et al.,
2020). Furthermore, none of these studies examined mediators of the developmental relations between internalizing and externalizing problems.
Within externalizing problems, there is an important distinction between non-aggressive and aggressive problems, where the latter are considered indicative of more serious issues by the time of adolescence (Fairchild & Smaragdi,
2018). Further, aggression may be particularly liable to impact relationship qualities because of its direct, confrontive and interpersonal nature (as compared to other forms of externalizing problems involving rule-breaking). However, most previous developmental cascade studies have focused on externalizing problems more broadly, leaving the specific role of aggression as a risk for and potential outcome of internalizing problems an important outstanding question.
Discussion
Previous studies have identified developmental cascades between internalizing and externalizing problems; however, the mediating mechanisms of these cascades are not fully understood. This is because these studies have tended to focus primarily on peer relationships and academic problems as mediators. Previous studies have also mostly relied on cross-lagged panel models that cannot disaggregate within- and between-person relations and there is a need to replicate these cascades in models that can isolate within-person developmental relations from potential between-person confounding. The results of the study suggested that neither peer relationships nor teacher relationships were significant mediators of internalizing-externalizing developmental cascades in isolation or in combination. The results did, however, suggest evidence of protective effects of positive peer and teacher relationships in early adolescence (age 11) on later internalizing problems (age 13). Importantly, the use of an ALT-SR (Curran et al.,
2014) to disaggregate within- and between-person effects, rather than the previously more commonly used CLPM, permits greater confidence that these protective effects are not due to the within-person-stable/between-person-varying confounds.
The lack of any evidence for developmental cascades between aggression and internalizing problems suggests no support for either the dual failure model (Capaldi,
1992) or the acting out (Carlson & Cantwell,
1980) model of externalizing-internalizing comorbidity in the current data. The current study is not the first to report null or mixed results in relation to these theoretical models. Blain-Arcaro and Vaillancourt (
2017), for example, found evidence for the dual failure model but not the acting out model. Meanwhile, other studies have found evidence for an externalizing-to-internalizing cascade consistent with the dual failure model but limited or no support for peer and academic problems as mediators (e.g., Leadbeater & Hoglund,
2009). However, as most previous studies have not used models that disaggregate within- and between-person effects, further work using longitudinal models such as RI-CLPM and ALT-SR will be helpful for clarifying the extent of empirical support for the dual failure and acting out models (Murray et al.,
2020).
The current study did, however, identify a novel protective effect of teacher relationships at age 11. This finding requires replication in future research but suggests that interventions to improve teacher-student relationships in early adolescence could help mitigate the risks for the emergence of internalizing problems in adolescence. Several previous studies (e.g., Driscoll & Pianta,
2010) evaluating interventions targeting teacher-student relationships have indicated promising results with respect to their positive impacts on child psychosocial outcomes. However, these studies have tended to focused on the impact of improving teacher-student relationship on externalizing problems in primary school children and the potential of teacher-student relationship interventions for the prevention of internalizing problems in adolescence has been little explored. It would also be beneficial to explore in future research which relationship aspects are most important in serving as protective factors for student mental health, for example, closeness, warmth, emotional support, or a lack of conflict (Pössel et al.,
2013).
The fact that the protective effect of teacher relationships was limited to the age 11 to age 13 lag may have a number of explanations. As adolescents move out of early adolescence, it is thought that the relative influence of adult support figures declines, while the influence of peers (Steinberg & Monahan,
2007) and intimate partners (Anderson et al.,
2015) increases, therefore, it is conceivable that it reflects a declining influence of teachers. However, the fact that the effect of peer relationships was also limited to the age 11 to age 13 lag suggests that the time-limitation of this protective effect is more reflective of a generalized critical period for relational (and perhaps broader) influences on internalizing problems. An attenuated influence of both teacher and peer relationships would also be consistent with the fact that the peak in onset of internalizing problems appears to be around 13-14 years of age (Kessler et al.,
2005), suggesting that the preceding period could be especially important for the effects of risk and protective factors.
The effect of peer relationships at age 11 on internalizing problems at age 13 replicates a large body of previous work suggesting that peer problems such as bullying victimization and rejection are important risk factors for internalizing problems (e.g., Arseneault,
2018). However, the current study is among only a small number to confirm that this association holds when taking into account possible between-person confounds (specifically factors that may vary between people but tend to be relatively stable within people over time). The current study, thus, adds important evidence for the negative impact of peer problems in early adolescence and further underlines the potential value of school-based programs to prevent peer problems such as bullying (Gaffney et al.,
2019).
It is important to highlight the limitations of the current study. First, the available measures of peer and teacher relationships were relatively brief. This meant that it was not possible to identify the specific aspects of peer problems (e.g., rejection) and teacher relationships (e.g., emotional support) that were the active ingredients in the protective effect of positive relationships on later internalizing problems. Second, the measurement waves were around two years apart, which may not correspond to the timescales over which the developmental cascades hypothesized play out. In particular, it may be that the interplay between aggression, internalizing problems, and peer and teacher relationships operates on a shorter timescale, resulting in an under-estimation of the importance of the pathways between these constructs in the current study. Indeed, almost all concurrent within-person covariances were significant in the ALT-SR. Future studies employing variable time measurement intervals could help address the question of the optimal time lag for capturing the interplay between aggression, significant relationships, and internalizing problems. The hypothesized timescale of effects is an aspect of developmental cascade models that is poorly specified, and further work should also focus on clarifying this. Third, the sample used in the current study was of a size such that precise gender-stratified estimates could not be obtained due to insufficient statistical power (based on Monte Carlo power analyses). Given that there are well established gender differences in internalizing problems and aggression, exploration of these relations in males and females separately will be important in future studies. Finally, the study sample was subject to some attrition and while previous analyses have suggested that drop-out was unrelated to previous levels of aggression and internalizing problems, it is not possible to be sure that it was “not missing at random” (NMAR) in missing data mechanism terms (Rubin,
1976). To the extent that the data were NMAR, estimates of model parameters will be biased in a difficult-to-predict direction.
Strengths of the present study include the use of a large, well-characterized community-ascertained longitudinal sample with relatively low levels of non-response and little non-random non-response (Eisner et al.,
2019); the application of statistical models that can disaggregate between- and within-person effects (Curran et al.,
2014); and the use of measures that have been shown to reliably measure a wide range of aggression and internalizing symptom levels (Murray et al.,
2019). This latter strength is important for ensuring that associations are not attenuated due to limited reliable ranges of measurement.
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