Intergenerational transmission of genetic risk for hyperactivity and inattention. Direct genetic transmission or genetic nurture?

Background: Hyperactivity and inattention, the symptoms of ADHD, are marked by high levels of heritability and intergenerational transmission. Two distinct pathways of genetic intergenerational transmission are distinguished: direct genetic transmission when parental genetic variants are passed to the child's genome and genetic nurture when the parental genetic background contributes to the child's outcomes through rearing environment. This study assessed genetic contributions to hyperactivity and inattention in childhood through these transmission pathways. Methods: The sample included 415 families from the Quebec Newborn Twin Study. Twins' hyperactivity and inattention were assessed in early childhood by parents and in primary school by teachers. The polygenic scores for ADHD (ADHD-PGS) and educational attainment (EA-PGS) were computed from twins' and parents' genotypes. A model of intergenerational transmission was developed to estimate (1) the contributions of parents' and children's PGS to the twins' ADHD symptoms and (2) whether these variances were explained by genetic transmission and/or genetic nurture. Results: ADHD-PGS explained up to 1.6% of the variance of hyperactivity and inattention in early childhood and primary school. EA-PGS predicted ADHD symptoms at both ages, explaining up to 1.6% of the variance in early childhood and up to 5.5% in primary school. Genetic transmission was the only significant transmission pathway of both PGS. The genetic nurture channeled through EA-PGS explained up to 3.2% of the variance of inattention in primary school but this association was non-significant. Conclusions: Genetic propensities to ADHD and education predicted ADHD symptoms in childhood, especially in primary school. Its intergenerational transmission was driven primarily by genetic variants passed to the child, rather than by environmentally mediated parental genetic effects. The model developed in this study can be leveraged in future research to investigate genetic transmission and genetic nurture while accounting for parental assortative mating.

Longitudinal study of childhood sleep trajectories and adolescent mental health problems.

Study Objective: To investigate whether childhood sleep trajectories are associated with mental health symptoms such as social phobia, generalized anxiety, depression, attention deficit hyperactivity disorder (ADHD), conduct problems, and opposition at age 15. Methods: A total of 2120 children took part in the Quebec Longitudinal Study of Child Development. Childhood sleep trajectories were computed from maternal reports at 2.5, 3.5, 4, 6, 8, 10, and/or 12 years. At age 15, 1446 adolescents filled out mental health and sleep questions. A path analysis model was assessed in the full sample. Results: Four childhood nocturnal sleep duration trajectories were identified: (1) a short pattern (7.5%), (2) a short-increasing pattern (5.8%), (3) a 10 hours pattern (50.7%), and (4) an 11 hours pattern (36.0%). Three childhood sleep latency trajectories were found: (1) a short pattern (31.7%), (2) an intermediate pattern (59.9%), and (3) a long pattern (8.4%). Finally, two childhood wakefulness after sleep-onset trajectories were found: (1) a normative pattern (73.0%) and (2) a long pattern (27.0%). The path analysis model indicated that children following a long childhood sleep latency trajectory were more likely to experience symptoms of depression (ß = 0.06, 95% CI: 0.01 to 0.12), ADHD (ß = 0.07, 95% CI: 0.02 to 0.13), conduct problems (ß = 0.05, 95% CI: 0.00 to 0.10) and opposition (ß = 0.08, 95% CI: 0.02 to 0.13) at age 15. Conclusions: This longitudinal study revealed that children presenting a long sleep latency throughout childhood are at greater risk of symptoms of depression, ADHD, conduct problems, and opposition in adolescence.

The intergenerational continuity of alcohol use in a population sample.

INTRODUCTION: Research shows that parental alcohol use predicts youths' alcohol use, but this intergenerational continuity may vary across countries, and little is known about its moderators. This study examined for the first time the intergenerational continuity in alcohol use in a population sample of families in Canada, and tested whether it varied by youths' sex, family income, or family structure. METHODS: We used prospective longitudinal data on 1632 families from the Quebec Longitudinal Study of Child Development (QLSCD), a representative sample from the province of Quebec, Canada. Youths self-reported alcohol use and binge drinking frequency at seven timepoints from early adolescence to early adulthood. Predictors were mothers' and fathers' self-reported alcohol use from youths' infancy through age 13, and mother-reported socioeconomic variables. RESULTS: We identified three trajectories of alcohol use from ages 13 to 21 years: normative, late-onset and early-onset. Maternal alcohol use increased the youths' risk of following the early-onset trajectory of alcohol use, while both parents' alcohol use decreased the odds of the youths following the late-onset trajectory, compared to the normative trajectory. Insufficient family income increased youths' risk of following either the early-onset or late-onset trajectories. Mothers' and fathers' alcohol use did not interact in predicting youths' trajectory, and we found no moderating effects of the youths' sex, insufficient income, or years as a single-parent family. CONCLUSION: The results suggest modest intergenerational continuity of alcohol use in Quebec families which may be used, with income insufficiency, to help identify at-risk children for targeted interventions.

Lability of prenatal stress during the COVID-19 pandemic links to negative affect in infancy.

The association between prenatal stress and children's socioemotional development is well established. The COVID-19 pandemic has been a particularly stressful period, which may impact the gestational environment. However, most studies to-date have examined prenatal stress at a single time point, potentially masking the natural variation in stress that occurs over time, especially during a time as uncertain as the pandemic. This study leveraged dense ecological momentary assessments from a prenatal randomized control trial to examine patterns of prenatal stress over a 14-week period (up to four assessments/day) in a U.S. sample of 72 mothers and infants. We first examined whether varied features of stress exposure (lability, mean, and baseline stress) differed depending on whether mothers reported on their stress before or during the pandemic. We next examined which features of stress were associated with 3-month-old infants' negative affect. We did not find differences in stress patterns before and during the pandemic. However, greater stress lability, accounting for baseline and mean stress, was associated with higher infant negative affect. These findings suggest that pathways from prenatal stress exposure to infant socioemotional development are complex, and close attention to stress patterns over time will be important for explicating these pathways.

A sequential model of the contribution of preschool fluid and crystallized cognitive abilities to later school achievement.

The present study documented in two distinct population-based samples the contribution of preschool fluid and crystallized cognitive abilities to school achievement in primary school and examined the mediating role of crystallized abilities in this sequence of predictive associations. In both samples, participants were assessed on the same cognitive abilities at 63 months (sample 1, n = 1072), and at 41 and 73 months (sample 2, n = 1583), and then with respect to their school achievement from grade 1 (7 years) to grade 6 (12 years). Preschool crystallized abilities were found to play a key role in predicting school achievement. They contributed substantially to school achievement in the early school years, but more modestly in the later years, due to the strong auto-regression of school achievement. They also mediated the association between fluid abilities and later school achievement in the early grades of school, with the former having modest direct contribution to the latter in the later grades. These findings are discussed regarding their implication for preventive interventions.

Calibrating temper loss severity in the transition to toddlerhood: Implications for developmental science.

The integration of neurodevelopmental perspectives into clinical science has identified irritability as an early dimensional marker of lifespan mental health risk. Elucidating the developmental patterning of irritable behavior is key to differentiating normative variation from risk markers. Accounting for dysregulation and contextual features of irritability is useful for differentiation at preschool age, laying the groundwork for even earlier characterization. We provide initial evidence for the validity of the Multidimensional Assessment Profile of Disruptive Behavior Temper Loss Scale, Infant-Toddler version in two independent samples of 12-18-month-olds from the US. We calibrated the measure using item response theory in a large representative sample, then validated within an independent sample. We characterized the developmental patterning of irritable behaviors and their dimensional spectrum, and demonstrated test-retest reliability, and convergent validity. The MAP-DB-IT is a standardized, dimensional survey assessing irritability that serves as a tool for characterizing the developmental expression of early mental health risk.

Early temperamental and biological predictors of dimensions of social withdrawal in childhood.

Social wariness and preference for solitude, two dimensions of social withdrawal, show unique associations with various socioemotional difficulties in childhood, including internalizing and peer problems. However, their early childhood predictors remain vastly undocumented. The present study aimed to examine whether early indicators of reactivity in situations of unfamiliarity such as behavioral inhibition, affect, and cortisol independently, or in interaction with emotion regulation as indexed by vagal tone, predict later social wariness and preference for solitude. Participants were 1209 children from the Quebec Newborn Twin Study. Vagal tone was assessed at 5 months, and behavioral inhibition, affect, and cortisol were assessed at 19 months in situations of unfamiliarity. Mothers, teachers, and peers evaluated social wariness and preference for solitude repeatedly from 4 to 10 years old. Findings show that three temperamental dimensions, social inhibition, nonsocial inhibition, and affect accounted for the variability in reactions to unfamiliarity. Behavioral inhibition to social unfamiliarity at 19 months predicted social wariness during the preschool years. Poor vagal regulation at 5 months exacerbated the risk associated with negative affect at 19 months to predict preference for solitude during the preschool years. Overall, results show that social wariness and preference for solitude may follow different developmental pathways.

Joint Consideration of Inhibitory Control and Irritability in Young Children: Contributions to Emergent Psychopathology.

Deficits in self-regulation capacity have been linked to subsequent impairment and clinical symptomology across the lifespan. Prior work has identified difficulty regulating angry emotions (i.e., irritability) as a powerful transdiagnostic indicator of current and future clinical concerns. Less is known regarding how irritability intersects with cognitive features of self-regulation, in particular inhibitory control, despite its mental health relevance. A promising avenue for improving specificity of clinical predictions in early childhood is multi-method, joint consideration of irritability and inhibitory control capacities. To advance early identification of impairment and psychopathology risk, we contrast group- and variable-based models of neurodevelopmental vulnerability at the interface of irritability and inhibitory control in contexts of varied motivational and emotional salience. This work was conducted in a longitudinal study of children recruited at well-child visits in Midwestern pediatric clinics at preschool age (N = 223, age range = 3-7 years). Group-based models (clustering and regression of clusters on clinical outcomes) indicated significant heterogeneity of self-regulation capacity in this sample. Meanwhile, variable-based models (continuous multiple regression) evidenced associations with concurrent clinical presentation, future symptoms, and impairment across the broad spectrum of psychopathology. Irritability transdiagnostically indicated internalizing and externalizing problems, concurrently and longitudinally. In contrast, inhibitory control was uniquely associated with attention-deficit/hyperactivity symptoms. We present these findings to advance a joint consideration approach to two promising indicators of neurodevelopmental vulnerability and mental health risk. Models suggest that both emotional and cognitive self-regulation capacities can address challenges in characterizing the developmental unfolding of psychopathology from preschool to early childhood age.

Home Visiting and Early Childhood Education for Reducing Justice System Involvement.

Early childhood intervention is particularly cost-beneficial when it reduces justice involvement, but ingredients that contribute to this outcome are unknown. The goal of this study was to estimate the effects of two common early childhood intervention ingredients-home visits and center-based education-on juvenile justice involvement. The Infant Health and Development Program (IHDP) randomized 1090 premature and low-birth-weight babies to intervention or control groups. Intervention group families were offered home visits from birth to age 3 years and high-quality center-based early childhood education from ages 1 to 3 years, but varied in their take-up of each intervention component. We estimated (1) intent-to-treat effects and (2) the effects of families' level of participation in each intervention component, using a novel stratification approach to minimize the impact of self-selection bias on dosage. Outcomes were children's risk of being stopped by police, arrested, or incarcerated, by age 18 years. Intent-to-treat analyses showed no effects of the IHDP for both sexes combined, nor for girls only, on any of the three outcomes, but there was an intent-to-treat effect on boys' risk of being arrested, OR = 0.43 (95% CI 0.24, 0.76). Analyses of dosage effects showed that, for both sexes combined, participation in the center-based educational component decreased the odds of being stopped by the police by 3% for each month of services. For boys only, the odds of being arrested decreased by 4% with each month of home visits and by 4% with each month of center-based educational services. We conclude that high-quality center-based early childhood education and, to some extent, home visits, reduce justice involvement among biologically vulnerable children, especially boys.

A window into racial and socioeconomic status disparities in preschool disciplinary action using developmental methodology.

There are large differences in expulsions and suspensions on the basis of race starting in preschool and divergent explanations for their cause. The current study explores how developmental methodology can shed light on this vexing issue. We leverage two measures: (1) childcare provider complaints about children's behavior and their recommended disciplinary action (measured by parent report); and (2) observed disruptive behavior measured by a laboratory-based standardized observation tool, the Disruptive Behavior Diagnostic Observation Schedule (DB-DOS), among a large, sociodemographically diverse sample of children (n  =$\text{=}$  430; mean age  =$\text{=}$  4.79 years). We identified three latent class profiles on the basis of race/socioeconomic status (SES) and found disparities in childcare provider complaints based on profile membership. More specifically, children classified in the Black/Hispanic, poor and Black, nonpoor profiles both had significantly higher childcare provider complaints compared with children in the White/Hispanic, nonpoor profile. By contrast, there were no differences in observed disruptive behavior based on race/SES profiles. Finally, childcare provider complaints in preschool were associated with lower cognitive performance in elementary school, above and beyond observed disruptive behavior in preschool and race/SES profiles. Implications for classroom practice and contributions to the national debate on school disciplinary policies are discussed.

Testing the effects of a prenatal depression preventive intervention on parenting and young children's self-regulation and functioning (EPIC): protocol for a longitudinal observational study.

BACKGROUND: Perinatal depression is a pervasive public health concern that disproportionately affects low-income women and can have negative impacts on parenting and child developmental outcomes. Few interventions focus on preventing perinatal depression. Previous studies suggest that Mothers and Babies is efficacious in preventing the worsening of depressive symptoms and the onset of postpartum depression. This manuscript presents the protocol of the EPIC study (Effects of a Prenatal Depression Preventive Intervention on parenting and young children's Self-Regulation and Functioning) to test the effects of Mothers and Babies on parenting and child developmental outcomes through 54 months postpartum. EPIC is an observational study that builds on a completed cluster-randomized trial (CRT). Innovations of this study are direct observations of a subsample of mother-child dyads and the inclusion of fathers/caregivers' variables as moderators of maternal mental health. METHODS: For this study, we plan to enroll 738 women with children under 30 months old, ≥18 years old, and who speak English or Spanish. Additionally, 429 fathers, partners, or other adult caregivers will be recruited through women participating in the study. Women will be recruited through the parent study (intervention and control participants) or through one of 10 home visiting programs in Illinois (control participants). Data collection will take place through maternal self-report at five time points (when the child is 30, 36, 42, 48, and 54 months), paternal self-report at three time points (when the child is 30, 42, and 54 months), and through mother-child observations at three time points (when the child is 36, 42, and 48 months). Outcome domains include maternal mental health, cognitive-behavioral and parenting skills, and child self-regulation and functioning. Moderators include the contributions of fathers/caregivers, race-ethnicity, and socioeconomic disadvantage. Power and sample size were calculated assuming a two-sided 5% type I error rate and assumed analyses on the individual level. DISCUSSION: This study has several key strengths and innovations, as well as great potential significance to influence the long-term trajectories of parenting and child development via prenatal intervention. TRIAL REGISTRATION: The study was retrospectively registered at ClinicalTrials.gov (Identifier: NCT04296734 ) on March 5, 2020.

Moving the dial on prenatal stress mechanisms of neurodevelopmental vulnerability to mental health problems: A personalized prevention proof of concept.

Prenatal stress exposure increases vulnerability to virtually all forms of psychopathology. Based on this robust evidence base, we propose a "Mental Health, Earlier" paradigm shift for prenatal stress research, which moves from the documentation of stress-related outcomes to their prevention, with a focus on infant neurodevelopmental indicators of vulnerability to subsequent mental health problems. Achieving this requires an expansive team science approach. As an exemplar, we introduce the Promoting Healthy Brain Project (PHBP), a randomized trial testing the impact of the Wellness-4-2 personalized prenatal stress-reduction intervention on stress-related alterations in infant neurodevelopmental trajectories in the first year of life. Wellness-4-2 utilizes bio-integrated stress monitoring for just-in-time adaptive intervention. We highlight unique challenges and opportunities this novel team science approach presents in synergizing expertise across predictive analytics, bioengineering, health information technology, prevention science, maternal-fetal medicine, neonatology, pediatrics, and neurodevelopmental science. We discuss how innovations across many areas of study facilitate this personalized preventive approach, using developmentally sensitive brain and behavioral methods to investigate whether altering children's adverse gestational exposures, i.e., maternal stress in the womb, can improve their mental health outlooks. In so doing, we seek to propel developmental SEED research towards preventive applications with the potential to reduce the pernicious effect of prenatal stress on neurodevelopment, mental health, and wellbeing.

The Early Childhood Irritability-Related Impairment Interview (E-CRI): A Novel Method for Assessing Young Children's Developmentally Impairing Irritability.

Irritability is a substrate of more than one dozen clinical syndromes. Thus, identifying when it is atypical and interfering with functioning is crucial to the prevention of mental disorder in the earliest phase of the clinical sequence. Advances in developmentally based measurement of irritability have enabled differentiation of normative irritable mood and tantrums from indicators of concern, beginning in infancy. However, developmentally sensitive assessments of irritability-related impairment are lacking. We introduce the Early Childhood Irritability-Related Impairment Interview (E-CRI), which assesses impairment associated with irritable mood and tantrums across contexts. Reliability and validity are established across two independent samples varied by developmental period: the Emotional Growth preschool sample (EmoGrow; N = 151, M = 4.82 years) and the When to Worry infant/toddler sample (W2W; N = 330, M = 14 months). We generated a well-fitting two-factor E-CRI model, with tantrum- and irritable mood-related impairment factors. The E-CRI exhibited good interrater, test-retest, and longitudinal reliability. Construct and clinical validity were also demonstrated. In both samples, E-CRI factors showed association to internalizing and externalizing problems, and to caregiver-reported concern in W2W. Tantrum-related impairment demonstrated stronger and more consistent explanatory value across outcomes, while mood-related impairment added explanatory utility for internalizing problems. The E-CRI also showed incremental utility beyond variance explained by the Family Life Impairment Scale (FLIS) survey indicator of developmental impairment. The E-CRI holds promise as an indicator of impairment to inform identification of typical versus atypical patterns reflecting early emerging irritability-related syndromes in the initial phase of the clinical sequence.

Linking the Child Behavior Checklist (CBCL) with the Multidimensional Assessment Profile of Disruptive Behavior (MAP-DB): Advancing a dimensional spectrum approach to disruptive behavior.

Disruptive behavior in childhood is common. It spans from normative child misbehaviors to clinically-significant and impairing problems. While there are many rating scales evaluating such behaviors, historically, measurement has emphasized counting the number of symptoms present rather than assessing the normal-abnormal spectrum of behavioral expression. This study uses data from 644 early school age children aggregated from two data sources to statistically link a commonly used symptom count measure, the Child Behavior Checklist (CBCL), to a more developmentally-sensitive measure, the Multidimensional Assessment Profile of Disruptive Behavior (MAP-DB). Two links between conceptually similar scales on each measure were developed: CBCL Conduct Problems and MAP-DB Aggression; and CBCL Oppositional Defiant Problems and MAP-DB Temper Loss. We compared two innovative methods-Item Response Theory (IRT) and Deming regression-to determine the optimal linking relationship. Results suggest IRT methods were superior in reducing linking error compared to Deming regression. While Deming regression accurately modeled the mean scores (thus minimizing linking bias), this method could not adequately address the floor effect for scores on the CBCL. For practical purposes, this study provides a crosswalk of score conversions between the CBCL and MAP-DB, such that data aggregation and group comparisons can be made across the two measures; this enables longitudinal analyses with historically-collected CBCL data to transition to the more innovative dimensional scales of the MAP-DB without undo loss of extant data. This study furthers efforts to shift from historical symptom counts to more developmentally-sensitive measurement across the disruptive behaviors spectrum.

Client attrition in the Nurse-Family Partnership® : Revisiting metrics of impact in a home visitation program in the United States.

The Nurse-Family Partnership® (NFP) is an evidence-based home-visiting program for low-income, first-time mothers. NFP® has demonstrated benefits for reducing child maltreatment and improving parenting, child development and families' economic self-sufficiency. It is now implemented widely in the US where, despite the use of home visits, which generally reduce barriers to program participation, only 35% of clients nationwide complete the 2.5-year program. This concurrent mixed-methods study was conducted in 2013 in an urban northeastern US NFP site and included administrative program data, surveys (n = 56), in-depth interviews (n = 14) with nurse home visitors, and focus groups with nurse supervisors (n = 13). We explored associations between nurses' attrition rates and their perspectives on client attrition and retention strategies. We further conducted an inductive thematic analysis of the qualitative data. Findings indicate that nurses' attrition rates were not significantly associated with their views and strategies to retain clients. Nurses and supervisors noted that clients' competing priorities and 'chaotic lives' primarily explained attrition. They thought that clients often left the program upon receiving enough information and skills or achieving key milestones, which may reflect reaching a saturation point, albeit prior to the full completion of the program. We offer recommendations to assess performance based on client accomplishments rather than whether they participated until the prescribed endpoint.

Genetic Correlation between Child Callous-Unemotional Behaviors and Fear Recognition Deficit: Evidence for a Neurocognitive Endophenotype.

This study investigates emotion recognition deficits as candidate neurocognitive endophenotypes for callous-unemotional (CU) behaviors. Using a twin design, we tested genetic correlations between child CU behaviors and poor processing of fearful and sad facial expressions. Participants were 504 twin pairs (209 MZ pairs; 295 DZ pairs) from the Quebec Newborn Twin Study, a longitudinal study of a population-based sample of twins. Teachers in kindergarten and first grade rated children's CU behaviors and other behavior problems (attention deficit and hyperactivity symptoms, physical aggression, and depressive symptoms). In first grade (mean age 7 years), the children completed the visual subtest of the Diagnostic Analysis of Nonverbal Accuracy Scale 2 (DANVA-II) to assess emotion recognition from facial stimuli. Using structural equation modeling, we examined the genetic-environmental etiology of the association between fear/sadness recognition and child CU behaviors, controlling for other behavior problems and recognition of other emotions. We found a significant genetic correlation between poor fear recognition and CU behaviors that was independent of other behavior problems. Poor recognition of sadness was not significantly associated with CU behaviors after taking into account other behavior problems. Our results suggest that CU behaviors and fear recognition have a partly shared genetic aetiology. This provides support for poor fear recognition as a key neurocognitive endophenotype for CU behaviors. Future research should test a hypothesized causal chain from specific genes, through amygdala functioning and fear recognition, to CU behaviors, and identify specific environmental factors (including intervention) that may disrupt this chain.

Relations Between Toddler Expressive Language and Temper Tantrums in a Community Sample.

This study examined the frequent clinical observation that toddlers with less expressive language have more severe temper tantrums. A representative sample of 2,001 mothers reported on their toddler's expressive vocabulary and frequency of different temper tantrum behaviors, a prominent feature of irritability and an emergent marker of mental health risk. Results revealed that 12- to 38-month-olds with fewer spoken words demonstrated more severe (frequent and dysregulated) temper tantrums. Toddlers who were late talkers at 24-30 months also had more severe tantrums; their relative risk of having severe tantrums was 1.96 times greater than peers with typical language. These results are the first to show that language and temper tantrums are related, and that this relation is present in the second year of life. These findings point to the importance of assessing both language and mental health risk in order to promote earlier identification and intervention for early childhood disorders.

Low-income mothers' entry into postsecondary education during middle childhood: Effects on adolescents.

This study tests whether young adolescents' achievement and behavior are associated with their mother's entry into post-secondary education (PSE) during their middle childhood years. It also examines five family processes that may link maternal PSE to development in middle childhood (income, home learning environment, mother's educational expectations for child, maternal presence, and family affective climate). The sample selects low-income families from the National Longitudinal Survey of Youth of 1979. Propensity score weighting adjusts for mothers' self-selection into PSE. We find that adolescents whose mothers entered PSE in their middle childhood scored higher than their peers on math, but similarly on reading, behavior problems, delinquency, and substance use. There were no associations between mothers' PSE entry and the proposed mediators.

Differentiating typical from atypical perpetration of sibling-directed aggression during the preschool years.

BACKGROUND: Sibling aggression is common and often viewed as benign. Although sibling aggression can be harmful for the victims, it may also be a marker of clinical risk for the aggressor. We differentiated typical from atypical levels of perpetration of sibling-directed aggression among preschoolers, a developmental period in which aggression is a normative misbehavior, by (a) identifying how frequently aggressive behaviors targeted at a sibling must occur to be psychometrically atypical; (b) mapping the dimensional spectrum of sibling-directed aggression from typical, more commonly occurring behaviors to rarer, more atypical, actions; and (c) comparing the psychometric atypicality and typical-to-atypical spectrum of sibling-directed aggression and peer-directed aggression. METHODS: Parents (N = 1,524) of 3- (39.2%), 4-(36.7%), and 5-(24.1%) year-olds (51.9% girls, 41.1% African-American, 31.9% Hispanic; 44.0% below the federal poverty line) completed the MAP-DB, which assesses how often children engage in aggressive behaviors. We used item-response theory (IRT) to address our objectives. RESULTS: Most aggressive behaviors toward siblings were psychometrically atypical when they occurred 'most days' or more; in contrast, most behaviors targeted at peers were atypical when they occurred 'some days' or more. With siblings, relational aggression was more atypical than verbal aggression, whereas with peers, both relational and physical aggression were more atypical than verbal aggression. In both relationships, the most typical behavior was a verbally aggressive action. Results were broadly replicated in a second, independent sample. CONCLUSIONS: These findings are a first step toward specifying features of sibling aggression that are markers of clinical risk and belie the notion that sibling aggression is inherently normative.