The goal of this study was to examine whether young adult offspring of depressed mothers display elevated levels of aggressive behavior at age 20, and to examine four family-level and individual-level factors that may mediate this association. The potential mediators tested in the current analyses were the quality of the parent-child relationship, exposure to maternal relationship dysfunction, youth social functioning, and youth depression. These questions were addressed using a two-wave longitudinal design in a community-based sample of mothers with varying depression histories and their offspring. The results suggested that a history of maternal depression prior to youth age 15 does predict higher levels of offspring aggression during the transition to adulthood. This association was fully mediated by youth depressive history. Three additional variables reflecting mother-child relationship quality, maternal romantic relationship quality and youth peer functioning were not significant mediators when taking into account the effects of youth depression.
The current finding that maternal depressive history predicts aggressive behavior among offspring is consistent with previous research demonstrating aggressive (Brennan et al., 2003
; Elgar et al., 2003
; Hay et al., 2003
; Kim-Cohen et al., 2005
; Langrock et al., 2002
; Malik et al., 2007
) and other externalizing (Anderson & Hammen, 1993
; Dawson et al., 2003
; Trapolini, McMahon, & Ungerer, 2007
) outcomes among children of depressed mothers. The current study is unique in suggesting that these effects may extend into later periods of development, even when accounting for the stability of prior aggression. It is essential to understand the predictors of aggression during this period of emerging adulthood, as individuals who do not desist from aggressive behavior before late adolescence are likely to engage in increasingly violent and dangerous behaviors (Elliot, 2000
; Loeber & Farrington, 1998
; Loeber & Hay, 1997
Aggression in young adulthood may also present unique risks to long-term psychosocial functioning, as the importance and nature of relationships with peers and romantic partners changes during this time, and new behavioral patterns of interaction may be established. Adolescents who are prone to negative affect may have difficulty navigating the increasingly complex relationships that are established during young adulthood, and may be more likely to experience conflict and react to that conflict in a maladaptive way. Furthermore, young adults with an aggressive interpersonal style may by choice or necessity select into relationships with peers who themselves have maladaptive interpersonal patterns, creating relationships that are likely to be characterized by conflict and perpetuate risk for negative psychosocial outcomes.
It is important to keep in mind that the current findings do not test change in aggressive behavior over late adolescence and are not specific to any specific trajectory of aggressive behavior, but apply to youth aggression during young adulthood in general. Previous research using a subsample of 370 adolescents from the current dataset found that maternal depression was predictive of both early-onset and adolescent-onset patterns of aggression and did not distinguish between these two trajectories (Brennan et al., 2003
). In fact, the current findings indicate significant stability of aggression between ages 15 and 20. Similar to prior longitudinal research describing a general trend towards desistance from aggression during adolescence (Cairns, Cairns, Neckerman, Ferguson, & Gariepy, 1989
; Stanger, Achenbach, & Verhulst, 1997
), the rates of clinically significant aggression in this study dropped between ages 15 and 20. However, there was notable continuity of relative levels of aggression within individuals. Spearman rank correlation tests show significant associations of rank ordered aggression scores at ages 15 and 20 by both mother (P =.70, p
<.001) and youth (P = .43, p
<.001) report. These findings suggest that the youth who were most aggressive at age 15 were also the most aggressive youth at age 20. The current study showed that youth depression is a strong predictor of aggression at age 20 even accounting for this intraindividual stability in relative levels of aggression.
Several potential mediators of the association between maternal depression and youth aggression were not significant. Three of these four met initial criteria as a candidate mediator when modeled individually.2
Maternal relationship conflict was the only proposed mechanism that did not predict youth aggression at age 20. Although some studies suggest that interparental conflict is an important mediator of youth adjustment among families with depressed parents (Cummings, Keller, & Davies, 2005
; Davies & Cummings, 1998
; Davies, Dumenci, & Windle, 1999
) other studies have not supported this hypothesis (Papp, Cummings, & Schermerhorn, 2004
; Trapolini, McMahon, & Ungerer, 2007
). It is possible that various youth outcomes are differentially related to marital conflict. Alternatively, it is possible that our ability to detect such a relationship may be limited by our measures of maternal relationship functioning. Although selected to reflect both physical and non-physical forms of conflict, at least two of the indicator variables may also capture other aspects of relationship quality, thereby obscuring a more precise influence of marital conflict. Finally, models examining the additive (Essex, Klein, Cho, & Kraemer, 2003
) or moderating (Papp, Goeke-Morey, & Cummings, 2004
) effects of interparental conflict may be more appropriate.
Of the four potential mediators examined, only youth depression by age 15 was a unique mediator of youth aggression at age 20. It is important to note that these effects of depression were found even when the effects of related impairments in youth social functioning and parent-child relationship quality were controlled. At least one previous study has found that adolescent depressive symptoms predict aggression one year later (Hale et al., 2008
). Additional research suggests that depression predicts a range of delinquent behaviors including aggression across adolescence, even when controlling for shared environmental risk factors (Beyers & Loeber, 2003
). The current findings suggest that this effect of depression on aggression extends into young adulthood, even accounting for levels of aggressive behavior in mid-adolescence.
In addition to the predictive relationship observed between depression at age 15 and aggression at age 20, there was also a strong cross-sectional relationship between depression and aggression at age 15. These findings are in line with previous studies demonstrating a moderate to strong correlation between depressive and aggressive symptoms in youth samples (Gjone & Stevenson, 1997a
; Hale, Vander Valk, Engels & Meeus, 2005
; Messer & Gross, 1994). The current study extends these findings by suggesting that even when this earlier association between aggression and depression and the stability of aggression is taken into account, youth depression remains a significant predictor of aggression in young adulthood. The association of depression with aggression both cross-sectionally and across developmental periods suggests that mood disorder history in adolescence may promote a stable and vicious cycle of aggressive behaviors and their concomitant negative outcomes among some youth.
Although clarification of the processes that account for the link between youth depression and aggression is beyond the scope of this project, several possibilities should be considered in future research. For example, shared genetic risk factors for depression and aggression may account for part of this association, as suggested by twin studies examining the overlap between depression and aggression that have implicated both genetic and environmental influences (Gjone & Stevenson, 1997a
; O’Connor, McGuire, Reiss, Hetherington, & Plomin, 1998
; Rowe, Rijsdijk, Maughan, Hosang, & Eley, 2008
; Subbarao et al., 2008
). The two conditions may also share biological risk factors, including decreased serotonergic activity and dopamine hyperfunction (Carver, Johnson, & Joorman, 2008
; Lahey, Hart, Pliszka, & Applegate, 1993
; Seo, Patrick, & Kennealy, 2008
A second potential explanation is underlying biologically and psychologically mediated deficits in emotion regulation that account for both early onset depression and aggressive behaviors. Previous research among child samples has found that difficulties with anger control are predictive of aggression (Chang, Schwartz, Dodge, & McBride-Chang, 2003
; Musher-Eizenman et al., 2004
). Symptoms such as irritability and hostility, which are common to both aggression and depression, may reflect this core deficit in regulation of negative affect. Further research with more direct physiological or self-report measurements of emotion regulation is needed to evaluate the hypothesis that emotional regulation difficulties may underlie both adolescent vulnerability to depression and risk for aggression in young adulthood. It is possible that poor emotion regulation skills may be a particularly important mechanism for aggression risk in this population given research suggesting a connection between the emotion regulatory abilities of parents and offspring (Carson & Parke, 1996
; Eisenberg & Fabes, 1994
Furthermore, the social experiences of depressed adolescents may contribute to the development or maintenance of an aggressive interpersonal style. Depressed youth are more likely than healthy peers to experience social rejection (Vernberg, 1990
), which may contribute to the development of the elevated rates of hostile attributional biases observed among depressed youth (Quiggle, Garber, Panak, & Dodge, 1992
). These biases in turn may increase the likelihood of aggressive behavior (Dodge & Coie, 1987
), which is likely to contribute to further rejection by peers (Juvonen & Gross, 2005
), thereby creating an escalating cycle of rejection and aggression. This pathway may account for both the cross-sectional and prospective relationships between depression and aggression. These risk processes may be particularly pronounced among depressed offspring of depressed mothers who are more likely than depressed offspring of nondepressed mothers to have negative cognitions about their own social abilities and higher levels of chronic interpersonal stress (Hammen & Brennan, 2001
; Hammen, Shih, Altman & Brennnan, 2003
). Further research is needed to explore these and other potential processes linking depression and aggression in youth.
In sum, these findings indicate that maternal depression by youth age 15 predicts overall levels of aggressive behavior at age 20. The relationship between maternal depression and youth aggression at age 20 was fully mediated through youth depressive symptoms by age 15, and this pathway remained significant even when accounting for the stability of aggressive behavior between ages 15 and 20. Theories regarding the well-established association between parental and offspring depression may need to be elaborated to account for an especially pernicious form of combined youth aggression and depression among some offspring. The functional outcomes of such youth need to be studied further in order to better understand the implications of depression-aggression comorbidity in adulthood.
An important limitation to the present analyses is that only one direction of causality between our predictor, mediator, and outcome variables was tested. It is likely that the true relationship between these variables is bidirectional and evolves over time. Unfortunately, the nature of the data collected in this project does not allow for a direct examination of how these relationships may unfold temporally. A longitudinal study beginning in early childhood with multiple waves of data collection is needed to address these issues more clearly. It is worth noting, however, that a recent study examining the relationship between adolescent aggression, depression, and parental rejection found that a uni-directional model predicting aggression from youth depression and parental rejection was a better fit than a bi-directional model (Hale et al., 2008
). Furthermore, longitudinal studies have shown that the pathway from depression to antisocial behavior is more robust than the pathway from antisocial behavior to depression (Beyers & Loeber, 2003
). Therefore, there is reason to suspect that the direction of causality tested in the current project is representative of a true effect of depression and family environment on aggression, even if other temporal relationships between these variables also exist.
An additional limitation was that not all potential mediators were tested. While an effort was made to consider both family-level and individual-level variables from a variety of domains considered to be important in the prediction of aggression, contextual variables and cognitive styles promoting aggression were not measured, nor were biological and genetic factors. In addition, the two-wave study design did not allow for the three waves of measurement that are the gold standard for tests of mediation (Cole & Maxwell, 2003
). The relatively modest CFI values for the mediational models must also be taken into consideration when evaluating these findings, although such values are not atypical among models with a large number of degrees of freedom.
Use of a community population that oversampled women with histories of depression may limit the generalizablity of these results. It is possible that somewhat different patterns would emerge in unselected samples. Furthermore, the majority of the aggression observed in the current study was within a developmentally normative range. These results may not apply to predictors of more serious violent behavior.
The present study expands upon the existing literature by demonstrating that maternal depression is an important predictor of aggression perpetrated by young adults. Although research on offspring of depressed mothers often focuses on the interegenerational transmission of depression, the current study suggests that aggression may be another important domain of adverse outcome that may have serious consequences for psychosocial functioning, including romantic relationship functioning (Keenan-Miller, Hammen, & Brennan, 2007
). The current findings may facilitate identification of individuals at high risk for aggression. Furthermore, the knowledge that this connection is mediated by youth depression suggests that interventions aimed at depression prevention and improvement of emotion regulation may be useful in decreasing aggression among at-risk populations. Given the high societal cost of aggression perpetrated by young adults, further research into the etiology and prevention is warranted.