Introduction
It is well established in the literature that externalizing behavior in childhood and adolescence is associated with a wide range of poor concurrent and longitudinal outcomes [
1]. Regarding longitudinal outcomes, studies report that children and adolescents with externalizing behavior problems are at risk for a wide range of disorders in adulthood that include: disruptive behavior [
2‐
7], mood and anxiety problems [
8‐
11], and substance use and abuse [
5,
9,
12].
However, because externalizing behavior is an umbrella concept encompassing several different kinds of behavior, Frick et al. [
13] performed a meta-analysis of 44 published studies and empirically divided externalizing behavior into four types: aggression (e.g., fights, bullies), oppositionality (e.g., temper, stubborn), property violations (e.g., lies, cruel to animals), and status violations (e.g., substance use, runaway). To our knowledge, only two studies have examined the adult outcome of types of externalizing behavior problems as suggested by Frick and colleagues [
13]. These studies underline the need to distinguish between types of externalizing behavior, that is, they report that status violations predict substance use and social impairment, that oppositionality only predicts social impairment, whereas property violations and aggression predict both substance use and risky sexual behavior [
15,
16].
Regarding development of externalizing behavior, previous studies have provided evidence for variation in developmental trajectories of externalizing behavior in childhood and adolescence with most studies identifying four to six distinctive trajectories [
17‐
19]. Developmental trajectories describe changes in both the level and the growth or decline of behaviors over time [
20]. It is important to know which change in level and growth across age may be considered normative for children and adolescents. Because from both theoretical and clinical perspective, it is indispensable to understand normal development for defining abnormal behavior at any age point. In the previous study that examined the development of the four externalizing behavior types suggested by Frick et al. [
13] from early childhood up to young adulthood (i.e., from age 4 to age 18) the following developmental trajectories were identified: three trajectories for aggression ranging from very low to high, six trajectories for oppositionality ranging from very low to high and including a trajectory where oppositionality increased in adolescence, and four trajectories for property and status violation ranging from low to high [
21]. Considering these different developmental trajectories of externalizing behavior that groups of children follow, it is important to examine groups of children that follow developmental trajectories that vary in level and shape, because an average developmental trajectory that describes expected development for most children may be considered insufficient. In the current study, we determined distinctive groups of individuals who are more likely to follow one developmental trajectory than another, within each type of externalizing behavior.
In the study by Bongers et al. [
21], status violations was the only externalizing behavior type that increased with age, whereas the remaining types primarily showed a persisting or decreasing course. In a more recent study by Bongers et al. [
15], in which the relation of both level and growth of externalizing problems, as suggested by Frick et al. [
13], to adult outcomes was examined, primarily the level of the trajectories was found to be predictive. Children with high-level trajectories of opposition and status violations reported more impaired social functioning, regardless of the direction, or growth, or decline of these high-level trajectories. However, in the study by Timmermans et al. [
16] both the level and growth of opposition, aggression, and property violations were related to poor adolescent outcomes such as risky sexual behavior and substance use. In this latter study only the level of status violations predicted later negative outcomes. Hence, findings are inconclusive as to how developmental trajectories of these externalizing behavior types are related to other long-term outcomes, and further research on this issue is needed.
In this study, we aimed to investigate associations between childhood externalizing behavior and adult psychopathology. We examined the prediction of adult DSM-IV disorders from developmental trajectories of the four types of externalizing behavior suggested by Frick et al. [
13] (i.e., opposition, aggression, property violations, and status violations) over a period of 24 years in a longitudinal, multiple birth cohort study of 2,076 children from the general population. Because studies have reported prognostic differences between the four types of childhood externalizing behavior as suggested by Frick et al. [
13], we investigated the linkage between childhood externalizing behavior and adult psychopathology, distinguishing these types of externalizing behavior. In addition, although previous studies reported outcomes for the four externalizing behavior types up to young adulthood (i.e., age 18 in the study by Timmermans et al. [
16]; up to age 30 in the study by Bongers et al. [
15]), knowledge about their outcome beyond young adulthood is lacking. Therefore, we aimed to extend the findings of Bongers et al. [
15], which are based on a previous wave of the current study, by examining the prediction of developmental trajectories in middle adulthood (i.e., from age 28 to 40 years).
Based on earlier findings, we expect that an elevated level of externalizing behavior in childhood has impact on the long-term outcome, in addition to the developmental course of externalizing behavior [
5,
8,
11,
15,
22,
23]. Furthermore, we expect that different types of externalizing behavior (i.e., aggression, opposition, property violations, and status violations) are related to different adult outcomes [
15,
16]. Finally, according to the fact that the oppositional and status violations type consist of more reactive and nondestructive behaviors, these types of problems are expected to develop into emotional problems. Because the property violations and aggression type consist of proactive, destructive behaviors, these types are expected to develop into behavior problems in adulthood [
24,
25]. Because behavior problems of the status violations type have been found to increase with age [
21], we expect that this type is associated with most adult problems.
Discussion
This study examined the relations between childhood trajectories of four distinctive types of externalizing behavior and DSM-IV disorders in adulthood in a longitudinal general-population sample that included males and females aged 4–16 years assessed at six time periods. All four types of externalizing behavior (i.e., aggression, opposition, property violations, and status violations) in childhood, showed associations with disruptive behavior in adulthood. Children displaying externalizing behavior of the oppositional type (e.g., arguing, disobedience, temper tantrums) also showed anxiety disorder in adulthood. Children in trajectories of the status violation type (e.g., runaway, truancy, drug, and alcohol use) showed primarily substance use, anxiety, and mood disorder in adulthood. Furthermore, we found that children who are in high-level externalizing behavior trajectories are most at risk to suffer from disorders in adulthood, that is, both internalizing and externalizing disorders. This 24-year follow-up study is unique in prospectively examining the adult outcomes of different developmental trajectories in four childhood types of externalizing behavior, in a large general-population sample of 1,399 children.
Consistent with results of previous longitudinal studies in the general population that investigated the long-term continuity of early externalizing behavior [
5,
14,
34], we can conclude that children with externalizing behavior are at increased risk for adverse outcomes in adulthood. Moreover, even after 24 years, children in all subtypes of externalizing behavior are at increased risk to suffer from internalizing and externalizing adult disorders. In addition, our study emphasizes the need to distinguish between the subtypes of externalizing behavior because we found differences between the predictive values of the different types of externalizing behavior. Of the four types of externalizing behavior, aggression (mainly including physical aggression) showed the least associations with adult psychopathology, whereas opposition and property violations mainly predicted adult disruptive disorder.
The status violations subtype was the weakest predictor for later disruptive behavior. However, children with behavior problems of this type showed substance use, anxiety, and mood disorder in adulthood. In a study that investigated which subtypes of externalizing behavior accounted for substance use [
16], it was also found that status violations predicts substance use in late adolescence. In our study, we found that even up to middle adulthood, strong associations were found between status violations and substance use. Studies that investigated the comorbidity between alcohol, drugs, and internalizing disorders reported that ‘self medication’ with alcohol or drugs was associated with an increased likelihood of anxiety disorders [
35,
36]. This verifies our finding of anxiety and substance use disorder in adulthood being related to status violations. Furthermore, another possible explanation for our finding of associations between childhood externalizing behavior types and adult internalizing disorders could be that the status violations and oppositional type comprise behaviors that are more reactive, nondestructive, and affective behaviors, and entail negative emotionality (e.g., anger, runaway, rule breaking), in contrast to aggression and property violations types that primarily comprise proactive and violent behaviors that are offensive and instrumental (e.g., bullying, vandalism). Proactive and reactive aggressions are two distinct subtypes of externalizing behavior and they have been found to differ in adult outcome. Proactive individuals tend to bully and be very unemotional, whereas reactive individuals show impulsive, angry responses to aversive events, particularly perceived by interpersonal threat [
24,
25]. In accordance with previous findings on reactive and proactive aggressive behavior, we found that children with more reactive, nondestructive externalizing problems (i.e., status violations and oppositional) suffer from later internalizing problems [
25,
37]
.
Because externalizing behaviors are expected to change largely in level and growth during childhood and adolescence [
5,
38], and are therefore best described from a developmental point of view [
39], we explored outcomes of trajectories of behavior in the current study, taking into account the developmental change through childhood and adolescence. We used LCGA to analyze trajectories of externalizing behavior, because this method is well adapted for modeling growth of phenomena within a population in which population members are not following a common developmental process of growth or decline. Consequently, we were able to report unique associations between distinctive developmental trajectories within every externalizing behavior type and adult internalizing and externalizing outcomes.
In accordance with findings of previous studies that investigated development of externalizing behavior, we found that children in high-level externalizing trajectories are most likely to suffer from adult problems [
5,
8,
11,
15,
22,
23]. Children in the most severe, high-level trajectory of opposition and property violations were almost four to five times more likely than children not displaying these problems to suffer from any disruptive behavior in adulthood. Findings of a study that investigated continuity of externalizing behavior up to the age of 32 show that externalizing individuals in a severe ‘life-course-persistent’ trajectory suffered from the most mental health problems [
5]. In a review of conduct disorder and its outcomes in general population studies it was found that increasing severity of externalizing behavior was associated with an increasing risk of an emotional disorder in adulthood [
11]. What this study adds to the literature is that we extend the above findings by confirming that high levels of externalizing behavior in childhood and adolescence are linked to poor outcomes in adulthood even up to age 40.
However, it should be noted that children in both low- and high-level trajectories of property violations showed persistence of externalizing behavior into adulthood in terms of having disruptive behavior in adulthood. This shows that children displaying behavior of the property violations type are at risk to suffer from adult problems, even if they develop through a low-level and decreasing trajectory during childhood and adolescence. Property violations comprise behaviors such as cruel to animals, fire setting, and vandalism. These behaviors are symptoms of both psychopathy and antisocial personality disorder [
32,
40], which are both very serious diagnoses. Possibly, the separate symptoms in this property violations type are that severe and radical, that even children who show relatively few of the symptoms comprising this property violations type, thus who develop through a low-level in this type, suffer from disruptive disorder in adulthood.
Limitations
Our findings should be interpreted in light of two limitations. First, although we achieved a relatively high response rate in a 24-year follow-up, a considerable proportion of the original sample from 1983 did not participate in this follow-up. By interpreting our results, one should be aware of the fact that in longitudinal population based studies, high-risk people are the most difficult to keep included. Although selective attrition effects were small in this study, some children with the most severe externalizing behavior problems were not included. Therefore, results may not generalize to high-risk populations. Consequently, studies on high-risk children are essential to complete the present findings on the predictive value of developmental trajectories of externalizing behavior. Second, the results of this study may have been influenced by time dependent environmental covariates, such as economic growth, ethnic distributions, or family structures that we did not control for.
Conclusions
Our study shows a relation between child to adolescent externalizing behavior and adult psychopathology, even over a 24 years time-interval. We can conclude that an elevated level of externalizing behavior in childhood has impact on the long-term outcome, regardless of the developmental course of externalizing behavior. Therefore, intervention and prevention should focus on individuals that show severe externalizing problems at any point in childhood or adolescence. Furthermore, we can conclude that different types of externalizing behavior (i.e., aggression, opposition, property violations, and status violations) are related to different adult outcomes, and it is therefore advisable to treat them separately. Mental health professionals working with children and adolescents with externalizing behavior should anticipate different developmental trajectories through life. Because children and adolescents with externalizing behavior of the status violations subtype were most likely to be affected in adulthood, we recommend that prevention and intervention should focus on children and adolescents showing behavior of this type such as substance abuse, truancy, and runaway.