We tested the effectiveness of the preventive behavioral parent training (BPT) program, The Incredible Years (IY), and the independent effects of previously suggested sociodemographic and intervention-based moderator variables (i.e., initial severity of externalizing problem behavior, child gender, social economic status, family composition, and number of sessions parents attended), in a large-scale randomized controlled trial. Questionnaire and observation data from 387 parents and children ages 4-8 years (M= 6.21, SD = 1.33, 55.30% boys) across pretest, posttest, and 4-month follow-up were analyzed, using full intention-to-treat analyses and correcting for multiple testing. IY was successful in decreasing parent-reported child externalizing behavior (Cohen's d = 0.20 at posttest, d = 0.08 at follow-up), increasing parent-reported (d = 0.49, d = 0.45) and observed (d = 0.06, d = 0.02) positive parenting behavior, and decreasing parent-reported negative parenting behavior (d = 0.29, d = 0.25). No intervention effects were found for reported and observed child prosocial behavior, observed child externalizing behavior, and observed negative parenting behavior. Out of 40 tested moderation effects (i.e., 8 Outcomes × 5 Moderators), only three significant moderation effects appeared. Thus, no systematic evidence emerged for moderation of IY effects. The present multi-informant trial demonstrated that many previously suggested moderators might not be as potent in differentiating BPT effects as once thought.

This study examined parent-observer discrepancies in assessments of negative child behavior and negative parenting behavior to shed more light on correlates with these discrepancies. Specifically, we hypothesized that informant discrepancy between observers and parents on child behavior would be larger when parents reported high levels of negative parenting (and vice versa) because high levels of these behaviors might be indicators of negative perceiver bias or patterns of family dysfunctioning. Using restricted correlated trait–models, we analyzed cross-sectional observation (coded with the Dyadic Parent-Child Interaction Coding System) and survey data (Eyberg Child Behavior Inventory and Parenting Practices Interview) of 386 Dutch parent-child dyads with children aged 4–8 years (Mage = 6.21, SD = 1.33; 55.30% boys). Small associations between parent-reported and observed child and parenting behavior were found, indicating high discrepancy. In line with our hypothesis, this discrepancy was higher when parents self-reported more negative parenting or more negative child behavior. Parent-observer discrepancy on negative child behavior was also predicted by child gender. For boys parents reported higher levels of negative child behavior than were observed, but for girls parents reported lower levels of negative child behavior than were observed. These findings suggest that informant discrepancies between observers and parents might provide important information on underlying, problematic family functioning and may help to identify those families most in need of help.

This study investigated whether children scoring higher on a polygenic plasticity index based on five dopaminergic genes (DRD4, DRD2, DAT1, MAOA, and COMT) benefited the most from the Incredible Years (IY) parent program. Data were used from a randomized controlled trial including 341 Dutch families with 4- to 8-year-old children (55.7% boys) showing moderate to high levels of problem behavior. IY proved to be most effective in decreasing parent-reported (but not observed) externalizing behavior in boys (but not girls) carrying more rather than fewer dopaminergic plasticity alleles; this Gene × Intervention effect was most pronounced in the case of boys whose parents' manifested the most positive change in parenting in response to the intervention. These results proved robust across a variety of sampling specifications (e.g., intention to treat, ethnicity).