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Additional file 1: Fig S1. Flow chart of participants included for analyses. Table S1. Parental age groups and child autistic-like traits (n = 5718). Table S2. Pearson correlation coefficients among variables. Fig S2.Quadratic graphs between parental age and child autistic traits at 5/6 years-of-age.Table S3. Association between maternal age and child autistic-like traits among mothers with parity of first pregnancy (N = 5,061). Fig S3. Quadratic graphs between maternal age and child autistic-like traits after adjusting for maternal characteristics. Fig S4. Polynomial Regression. Fig S5. Spline Regression.

The Dysregulation Profile (DP) has emerged as a measure of concurrent affective, behavioral and cognitive dysregulation, associated with severe psychopathology, and poor adjustment. While originally developed with the Child Behavior Checklist, more recently the DP has also been defined on the Strengths and Difficulties Questionnaire (SDQ), mostly with a 5-item, but also a 15-item, SDQ-DP measure. This study evaluated the SDQ-DP by examining its factor structure, measurement invariance, and construct validity. Different SDQ-DP operationalizations were compared. In a United States longitudinal community sample (N = 768), a bifactor model consisting of a general Dysregulation factor and three specific factors of Emotional Symptoms, Conduct Problems, and Hyperactivity-Inattention fitted best, across three different developmental periods (early childhood, middle childhood, and adolescence) and across three different reporters (parents, teachers, and youth). Measurement invariance across reporter, gender, and developmental period was demonstrated. These findings indicate that the SDQ-DP, like the CBCL-DP, reflects a broad syndrome of dysregulation that exists in addition to specific syndromes of emotional symptoms, conduct problems, and hyperactivity-inattention. SDQ-DP bifactor scores were strongly related with scores on the 5- and 15-item SDQ-DP measures and similarly concurrently associated with two markers of self-regulation, ego-resiliency and effortful control, and longitudinally with antisocial behavior and disciplinary measures. As reliability, validity, and stability was weaker for the SDQ-DP 5-item measure, use of all 15 items is recommended. Advantages of using a bifactor approach are discussed as well as the potential of the SDQ-DP as an easy screening measure of children at risk for developing serious psychopathology. (PsycINFO Database Record

The general factor of psychopathology (GP, or p factor) and the Dysregulation Profile (DP) are two conceptually similar, but independently developed approaches to understand psychopathology. GP and DP models and their stability, antecedents and outcomes are studied in a longitudinal sample of 1073 children (49.8% female). GP and DP models were estimated at ages 8 and 14 years using the parent-reported Child Behavior Checklist (CBCL) and Youth Self Report (YSR). Early childhood antecedents and adolescent outcomes were derived using a multi-method multi-informant approach. Results showed that the general GP and DP had similar key symptoms and were similarly related to early-childhood antecedents (e.g., lower effortful control, higher maternal depression) and adolescent outcomes (e.g., reduced academic functioning, poorer mental health). This study demonstrates that GP and DP are highly similar constructs in middle childhood and adolescence, both describing a general vulnerability for psychopathology with (emotional) dysregulation at its core. Scientific integration of these approaches could lead to a better understanding of the structure, antecedents and outcomes of psychopathology.

OBJECTIVE: High co-occurrence of externalizing and internalizing problems could underlie inconsistent findings regarding the relation between heart rate (HR) and psychopathology. In this study, HR measures were examined in relation to a general dysregulation profile studied from variable- and person-centered approaches. METHOD: The sample (N = 182) consisted of 8- to 12-year-old children referred for externalizing behaviors and typically developing children (mean age 9.70, SD 1.26; 75.8% boys). Resting HR (HRrest) was assessed during a 3-minute resting period. HR reactivity (HRreactivity) was assessed during an emotionally evoking go/no-go task. RESULTS: From a variable-centered approach, a bifactor model was fitted with a general factor of dysregulation underlying symptoms of anxiety/depression, aggression, and attention problems. HRrest was positively associated with dysregulation and specific aggression. From a person-centered approach, a latent profile analysis was used to identify different psychopathology classes: normative (n = 92), predominantly aggressive (n = 69), and dysregulated (n = 14). The latter was characterized by co-occurring increased levels of anxiety/depression, aggression, and attention problems. HRrest was increased in the predominantly aggressive class and HRreactivity was increased in the dysregulated class. CONCLUSION: High HRrest, or (trait-like) over-arousal, seems to be associated with dysregulation rather than uniquely associated with low externalizing or high internalizing symptomatology. In addition, HRrest predicted greater aggression and HRrest was increased in the predominantly aggressive class. High HRreactivity, or enhanced emotional reactivity, might be characteristic for a clinically relevant dysregulated subgroup. Assessment of HR could provide additional knowledge on individual differences that can help refine diagnostics and intervention efforts.

Negative thinking is seen as an important mediating factor in the development of prolonged grief disorder (PGD), a syndrome encompassing debilitating symptoms of grief. No measure of specific grief related cognitions is available yet. Based on an adult measure of negative thinking in adults we developed a questionnaire for children, the Grief Cognitions Questionnaire for Children (GCQ-C). This study investigated several psychometric properties of the GCQ-C. Both reliability and validity were investigated in this study, in which hundred fifty-one children and adolescents (aged 8–18 years) participated. Findings showed that items of the GCQ-C represented one underlying dimension. Furthermore, the internal consistency and temporal stability were found to be adequate. Third, the findings supported the concurrent validity (e.g., significant positive correlations with self-report indices of PGD, depression and posttraumatic stress disorder), convergent and divergent validity of the GCQ-C. This study provides further evidence for the importance of negative thinking in PGD in children and adolescents.

This study examined trajectories of aggression and rule breaking during the transition from childhood to adolescence (ages 9–15), and determined whether these trajectories were predicted by lower order personality facets, overreactive parenting, and their interaction. At three time points separated by 2-year intervals, mothers and fathers reported on their children's aggression and rule breaking (N = 290, M age = 8.8 years at Time 1). At Time 1, parents reported on their children's personality traits and their own overreactivity. Growth mixture modeling identified three aggression trajectories (low decreasing, high decreasing, and high increasing) and two rule-breaking trajectories (low and high). Lower optimism and compliance and higher energy predicted trajectories for both aggression and rule breaking, whereas higher expressiveness and irritability and lower orderliness and perseverance were unique risk factors for increasing aggression into adolescence. Lower concentration was a unique risk factor for increasing rule breaking. Parental overreactivity predicted higher trajectories of aggression but not rule breaking. Only two Trait × Overreactivity interactions were found. Our results indicate that personality facets could differentiate children at risk for different developmental trajectories of aggression and rule breaking.

This study examined separate developmental trajectories of anxious and depressive symptoms from childhood to adolescence (9–15 years) in a community-based sample (N= 290). At three measurement points, mothers and fathers reported on their children's anxious and depressive symptoms, and at Time 1 they reported on lower order child personality facets and on their parenting. By means of growth mixture modeling, three developmental trajectories were identified for anxious symptoms: steady low (82%), moderate increasing–decreasing (5.9%), and high declining groups (12.1%). For depressive symptoms, two developmental trajectories were found: steady low (94.1%) and moderate increasing groups (5.9%). Higher shyness, irritability, and altruism predicted membership in more problematic anxious and depressive groups. The personality facets energy, optimism, compliance, and anxiety were unique predictors for class membership for anxious symptoms, and the effects of shyness, irritability, and compliance were moderated by overreactive parenting. Shyness and irritability increased the probability of following the moderate increasing–decreasing anxiety trajectory, but only in the context of high or average levels of overreactive parenting. Compliance increased the probability of following the moderate increasing–decreasing and high decreasing trajectories in the context of high overreactive parenting. Our results indicate that childhood personality facets differentiate trajectories of anxious and depressive symptoms in theoretically compelling ways.

Objective The aim of the present study was to examine the moderating role of Big Five personality traits in short and long term effectiveness of MultiSystemic Therapy (MST) for serious and persistent juvenile delinquents. Method Data of a randomized controlled trial ( N = 256) were used to examine the research question. Results Extraversion, Emotional Stability and Openness did not moderate short term effectiveness of MST, but Conscientiousness and Agreeableness did: MST was most effective for highly conscientious and highly agreeable juvenile delinquents. Personality did not moderate the effectiveness of MST on aggression or the long-term effectiveness of MST. Conclusion This study shows the importance of personality traits for short-term treatment outcomes, effectiveness of MST differs for high/low Agreeableness and Conscientiousness.

This study examined the prospective relationship between childhood Big Five personality characteristics and perceived parenting in adolescence. In addition, we investigated whether this relationship was mediated by parental sense of competence, and whether associations were different for mothers and fathers. For 274 children, teachers reported on children’s Big Five personality characteristics at Time 1, mothers and fathers reported on their sense of competence at Time 2, and the children (who had now become adolescents) rated their parents’ warmth, overreactivity and psychological control at Time 3. Mediation analysis revealed both direct and indirect effects. No differences in associations were found for perceived parenting of mothers and fathers. This study demonstrates that child personality in late childhood is significantly related to perceived parental warmth, overreactivity and psychological control in adolescence. In addition, parental sense of competence mediates the relationship between child conscientiousness and perceived parental warmth, overreactivity and psychological control.

Recently, a phenotype of severe dysregulation, the Dysregulation Profile (DP), has been identified. DP consists of elevated scores on the Anxious/Depressed (AD), Aggressive Behavior (AGG) and Attention Problems (AP) scales of the Child Behavior Checklist (CBCL), Teacher Report Form (TRF), or Youth Self Report (YSR). A drawback in current research is that DP has been conceptualized and operationalized in different manners and research on the factor structure of DP is lacking. Therefore, we examined the factor structure of DP across multiple reporters, measurement invariance across gender, parents, and time, as well as links between DP and self-harm and suicidal ideation. Data from a large community sample were used (N = 697), covering middle childhood (Mage = 7.90, (SD = 1.16) and adolescence (Mage = 13.93, SD = 1.14). Mothers, fathers, teachers, and youth themselves reported on children’s emotional and behavioral problems using the CBCL, TRF, and YSR. Results indicated that in middle childhood and in adolescence, a bifactor model with a general factor of Dysregulation alongside three specific factors of AD, AGG, and AP fitted best, compared to a second-order or one-factor model. The model showed good fit for mother, father, teacher, and youth reports and showed invariance across gender, parents and time. Youth, mother, and father reported Dysregulation was uniquely and positively related to adolescent-reported self-harm and suicidal ideation. The DP is best conceptualized as a broad dysregulation syndrome, which exists over and above anxiety/depression, aggression, and attention problems as specific problems. The bifactor model of DP explains the uniqueness and interrelatedness of these behavioral problems and can help explaining shared and non-shared etiology factors. The exclusive link between the general dysregulation factor and adolescents’ self-harm and suicidal ideation further established the clinical relevance of the bifactor model.

The aim of this study was to determine whether two risk factors that are frequently selected as targets for prevention and intervention purposes—involvement with deviant peers and parent–adolescent relationship quality—are associated with delinquent behavior in the same way in a juvenile general population sample ( n = 88) as in a juvenile offender sample ( n = 85). Information on delinquency and the quality of parent–adolescent relationship was obtained from adolescents and parents. The results of path analyses showed that relations between poor parent–adolescent relationship quality, involvement with deviant peers, and delinquency depended on whose point of view is used (adolescent or parent) and which sample is used (general population or delinquent sample). These findings indicate that caution is warranted when theories based on research with community samples are used for development of intervention programs for juvenile delinquents.

This dissertation reports on a study on the effects of secure residential youth care on the behavioral problems, trauma problems, emotion regulation problems and problems in perceived competence of adolescents and the parenting problems of their parents or educators. In addition, this study explores the treatment needs of these adolescents and investigates possible alternative interventions for secure residential youth care.

Many efforts have been made to prevent the occurrence or recurrence of child abuse. However, these preventive efforts have not yet resulted in a decrease of child abuse over time. Furthermore, review studies on the effectiveness of preventive interventions for child abuse showed only limited overall effects of the currently available interventions. The important question arising from this state of affairs is: what can be done to strengthen preventive efforts to stay ahead of child abuse? Seeking an answer to this question was the aim of the present dissertation. Specifically, the studies of this dissertation are focused on: identifying individual components of parent training programs (Chapter 2), home visiting programs (Chapter 3), and school-based prevention programs (Chapter 4 and 5) that are effective in preventing or reducing (the risk of) child abuse; examining current child abuse detection and reporting behavior of healthcare and education professionals and identifying potential improvements that may lead to better child abuse detection and reporting (Chapter 6); and exploring the potential of administrative child welfare data in evaluating the long-term benefits of preventive early childhood interventions (Chapter 7).

Many children and adolescents referred to clinical mental health institutions present a complex picture of co-occurring internalizing problems (e.g. anxiety) and externalizing problems (e.g. aggressive behavior). These ‘dysregulated’ children have problems with regulating affect, behavior and cognition, and are at increased risk for maladaptive outcomes. The DP has emerged as a reliable and valid measure of the complex phenotype of dysregulation and is generally defined by elevated scores on three syndrome scales of the Child Behavior Checklist (CBCL), namely the Anxious/Depressed, Aggressive Behavior and Attention Problems (or AAA-)scales. The CBCL is a well-known and widely used parent-reported instrument to chart behavioral and emotional problems of children and adolescents. In this dissertation, five empirical studies on the DP are presented, utilizing four different data sets from three countries (Belgium, Canada, United States). A multi-method and multi-informant approach were adopted. The first aim was to examine the conceptualization and measurement of the DP. Results from factor analyses revealed that a bifactor model best described the profile structure of the AAA-scales that comprise the DP. A bifactor model is a hierarchical model where items (symptoms) load on both on a general underlying factor of Dysregulation as well as one of three specific factors of Anxiety/Depression, Aggressive Behavior or Attention Problems. The same result was found across samples, instruments (CBCL and Strengths and Difficulties Questionnaires), developmental periods (early childhood, middle childhood and adolescence), and reporters (mothers, fathers, teachers, youth themselves). As such, this dissertation provides robust evidence that the DP can best be conceptualized as a broad syndrome of dysregulation which exists over and above specific problems related to affect, behavior, and cognition. This bifactor model bears strong resemblance to models of a ‘general factor of psychopathology’ (GP or ‘p factor’), and integration of both fields of literature is thus warranted. The second aim was to examine stability and change of the DP. Findings showed that across different samples, relative stability of the DP (i.e., the extent to which the relative differences in the DP among children remain the same over time) was strong for parent-reported DP and moderate for teacher-reported DP. The specific factors such as Anxiety/Depression were only weak to moderately stable. This suggests that while dysregulation, as a general vulnerability for developing different forms of psychopathology, is more stable than its specific manifestations. While homotypic continuity (e.g., dysregulation predicting dysregulation at a later time point) was strongest, there was also evidence for heterotypic continuity. This indicates that specific manifestations of psychopathology (e.g., anxiety/depression) increase risk of comorbid psychopathology (i.e., dysregulation) across time and vice versa. Furthermore, in this general population sample, the DP was found to follow a nonlinear developmental course, peaking in early adolescence. Specifically, DP scores increased from age 4 to 11, and then decreased (which looks like an inverted U-shape). The third aim was to investigate early childhood antecedents, adolescent outcomes and psychophysiological correlates of the DP. This dissertation further established the DP as a broad risk marker, as we found that the DP predicted a range of negative outcomes including personality pathology, mental health problems, and psychosocial maladjustment. We added to a scarce body of research on antecedents by showing that the DP is predicted by early temperament and self-control, and family factors including maternal depression and parenting. Exploratory findings showed that the DP was linked to higher resting heart rate, reflecting chronic overarousal.

Approximately 6400 children and adolescents lose a parent in the Netherlands and even more children are confronted with other types of loss such as the death of a close friend or grandparent. The death of a loved one is one of the most devastating events that can occur in children’s and adolescents’ lives. There is growing recognition of a syndrome that children can develop post loss, referred to as Prolonged Grief Disorder (PGD). This dissertation project had three aims: (I) to increase our understanding of the phenomenology and correlates of PGD, (II) to enhance knowledge on the role of negative thinking in the development of PGD in children and (III) to develop an intervention for children who suffer from loss and to examine its feasibility an potential efficacy. Three studies were conducted to investigate the first aim. First we developed the Inventory of Prolonged Grief for Children (IPG-C) and the Inventory of Prolonged Grief for Adolescents (IPG-A). Findings suggest that both inventories have good internal consistency, stability and concurrent validity. Both can be used for the assessment of PGD in children and adolescents who suffer from loss and also for treatment studies among bereaved children. In a second study we found that PGD, depression and Posttraumatic Stress Disorder (PTSD) are distinct constructs in children who suffer from bereavement. Our third study suggested that avoidance symptoms of bereavement-related PTSD may better be conceived as two separate clusters of effortful avoidance and symptoms of emotional numbing. Beside those main findings we found that correlations between children’s ratings and parent-ratings on grief related feelings are moderate. This indicates that it is important that children report about their own grief instead of solely relying on their parents’ observations of the suffering following a loss. In order to understand why some children cope with loss more easily than others (our second aim), it is also important to study the role of negative thinking among bereaved children. However, no measure was available. To fill this gap, we developed the Grief Cognition Questionnaire for Children (GCQ-C). Findings suggest that it is a reliable and valid tool to examine negative grief related cognitions in children and adolescents. Despite the fact that some children suffer from grief related problems and that there is a growing recognition of PGD, hardly any effective treatments are available. We therefore developed Grief-Help, a cognitive behavioural treatment that consists of nine (weekly) sessions for the child and five separate (two-weekly) sessions for their parent(s). We tested Grief-Help in two separate pilot studies. Based on those studies the treatment appears promising enough to warrant evaluation in a controlled trial. Such a multicentre Randomised Controlled Trial therefore is currently being conducted in the Netherlands.

The overall aim of this dissertation was to examine how child temperament and personality change, what the role of parenting is in explaining these changes, and how child temperament/personality and parenting together predict child internalizing and externalizing problems. In this dissertation, we took both a person-, and a variable-centered approach to the study of temperament and personality. Taking a person-centered approach, we showed that the personality types often found in research on personality in older children (i.e., a resilient/well-adjusted type, an overcontrolled type that experiences internalizing problems, and an undercontrolled type that exhibits externalizing problems) are also present in temperament configurations in toddlerhood, and that they can be obtained from multiple informants’ reports of personality in childhood. Additionally, we showed that, although temperament traits are only moderately stable in toddlerhood, temperament types are highly stable at this age already. Taking a different person-centered approach, we identified a small group of children whose personality configurations became increasingly extreme across development. Although personality types usually do not add much predictive value over dimensions, the probability of belonging to this increasingly extreme group was predictive of internalizing and externalizing problems, above and beyond levels of the personality dimensions. Taking a variable-centered approach, we showed that children’s mean-level personality development was temporarily aimed at becoming less mature: mean levels of extraversion, benevolence, conscientiousness, emotional stability and imagination decreased across the transition to adolescence, with levels of benevolence, conscientiousness and imagination increasing again from mid-adolescence onwards. Although changes were small, we found that decreases in extraversion and emotional stability were predictive of internalizing problems, and that decreases in benevolence, conscientiousness and emotional stability were predictive of externalizing problems. Results of our studies further showed that inter-individual differences in temperament and personality (change) were associated with parenting, with more associations found for warm/supportive parenting than for hostile/overreactive parenting. Child temperament/personality was more important in determining parenting behavior (“child effect”), than vice versa (“parent effect”). However, most evidence was found for associated change (“parallel processes”), indicating that if either the child or the parent changes, the other changes in order to adjust. Finally, we investigated how child temperament and personality are interrelated with parenting in the etiology of internalizing and externalizing adjustment problems. We found that, in addition to being associated with temperament and personality change, overreactive parenting predicted heightened adjustment problems in children, both independently and in interaction with child personality. Additionally, we investigated parent-child interaction processes as they unfold in real-time, and found that when mother-child interaction was characterized by a high degree of variability in affective expressions, children experienced more internalizing and externalizing problems. In conclusion, the findings of this dissertation indicate that children’s temperament/ personality configurations are highly stable, but that mean-level changes in dimensions occur. Inter-individual differences in changes in temperament/personality and parenting are associated, and together are important in determining a child’s risk for internalizing and externalizing adjustment problems.

Stable externalizing behavior in childhood places children at risk for the development of a chronic and persistent pattern of externalizing behavior problems. Preventive interventions that aim to interrupt this developmental trajectory are crucial. Until now, no evidence-based intervention for children with elevated levels of externalizing behaviors existed in the Dutch School context. First, we conducted a meta-analysis on international studies of school-based indicated interventions and found that individually delivered interventions are effective in reducing externalizing behavior (d = .28), increasing prosocial behavior (d = .43) and changing social cognitive functioning (d = .82). Next we examined the effectiveness of Stay Cool Kids, a preventive intervention for externalizing behavior. Moreover, we tested for whom and how the intervention works. This study used a cluster Randomized Controlled Trial with 48 elementary schools (264 fourth-grade children with elevated levels of externalizing behavior)in the Netherlands, that were randomly assigned to the intervention or no-intervention control condition. Results showed that Stay Cool Kids reduced reactive and proactive aggressive behavior (mean effect sizes on aggressive behavior were .22, .29, .25 and .21 according to children, teachers, mothers, and fathers, respectively). Moreover, the effect of the intervention was clinically significant, because participation in the intervention resulted in differences in the child’s functioning from clinical to sub-clinical or normative levels of externalizing behavior according to teachers. Some aspects of problems in social cognitive functioning were reduced (approval of aggression, d = .22) and children showed more positive self-perception (d = .49). The results of follow-up assessment showed that Stay Cool Kids resulted in sustained reduction in teacher reported aggression, when children moved to fifth grade. Results from the moderation analyses showed that boys, immigrant Dutch children, children who are moderately conscientious (organized and planful) and less extraverted (sociability and agency) benefitted more from the intervention on specific outcomes at short-term. In addition, less extraverted children showed stronger intervention effects immediately after the intervention, and effects at follow-up were stronger for these children. Tests of the theoretical model of Stay Cool Kids, proposing that changes in social cognitions would lead to changes in behavior, revealed that an increase in positive self-perception resulted in a decrease in child aggressive behavior. Child participation in the intervention resulted in an increase in maternal involvement, which in turn resulted in decreases in aggression. Altogether, the studies in this dissertation show that Stay Cool Kids can reduce externalizing behavior (reactive and proactive aggression, clinical externalizing behavior) across settings (school and home), in boys and girls and in children with different ethnic backgrounds. Effect sizes of Stay Cool Kids were similar to findings in international meta-analyses and can be considered as small to medium. It is important to realize that (maintenance of) effects of the intervention were not the same for all children. These results underline the importance of personalized mental health care adapted to children’s specific needs.

Current theories and models on child development emphasize that children and their environmennt form a system with bidirectional processes of interactions. Transactional models, which integrate parent and child effects, may be especially successful in describing and explaining the development of problem behaviour in children and adolescence. In line with this perspective, this dissertation examined how aggressive and rule-breaking (externalizing) behaviours develop between childhood and adolescence (6-17 years), to what extent individual-level factors (child personality) and proximal contextual factors (parent personality, parenting behaviour) may help to explain their development, and how the development of these risk factors can be described and explained. The results of this dissertation are based on a large-scale, longitudinal study about externalizing behaviours, parenting, and parent and child personality characteristics (Flemish Study on Parenting, Personality, and Development). Mothers, fathers, teachers, and children filled out questionnaire for up to six times between 1999 and 2009. Further, data was used of a South Korean study, for which mothers of young children filled out questionnaires about their personality characteristics, parenting, and feelings of parental competence. Results showed that overall, children decreased in aggression and increased in rule-breaking behaviours, and parents on average decreased in overreactive discipline and warmth as children transitioned to adolescence. Interindividual differences in rates of changes were partly explained by initial levels in the respective behaviours when children were still young. Specifically, if children or parents initially showed more externalizing behaviours or overreactive discipline, they decreased less in externalizing and overreactive behaviours over time. Parents, who exhibited less warmth initially, decreased more in warmth over time. Further, overreactive and warm parenting in childhood were related to changes in externalizing behaviours across ten years and vice-versa. More than parenting, however, child personality explained why children changed in certain ways. First, child personality was related directly to the development of externalizing behaviours across ten years. Second, child personality was related to later parenting, which in turn was related to externalizing behaviours. Third, child personality shaped how overreactive discipline was related to the development of externalizing behaviours. Regarding the explanation of parenting, our results showed that parents’ personality was more important for overreactive discipline than child personality was, but parent and child personality were similarly important for warmth. Additionally, child aggression and parent personality were related to parental feelings of competence and closeness to the child, which in turn were associated with overreactive and warm parenting. To summarize, this dissertation shows that differences between children regarding the development of externalizing behaviours are to a large extent explained by the development of parenting as children transition into adolescence. Moreover, child personality plays an essential role in the development of externalizing behaviours, both directly and in concert with parenting. Taking into account both individual child characteristics and parenting behaviours may substantially improve our understanding of externalizing behaviours.