In the current meta-analysis, we investigated the link between child and adolescent sibling relationship quality (warmth, conflict and differential treatment) and internalizing and externalizing problems, and potential moderators of these associations. From 34 studies, we obtained 85 effect sizes, based on 12,257 children and adolescents. Results showed that more sibling warmth, less sibling conflict and less differential treatment were all significantly associated with less internalizing and externalizing problems. Effect sizes for sibling conflict were stronger than for sibling warmth and differential treatment, and associations for internalizing and externalizing problems were similar in strength. Effect sizes were moderated by sibling gender combination (stronger effects for higher percentage brother pairs), age difference between siblings (stronger effects for smaller age differences), and developmental period (stronger effect sizes for children than for adolescents). These results indicate that the sibling context is important when considering psychopathology. In addition to the overwhelming evidence of the impact of parent-child and marital relationships on child and adolescent development, the present meta-analysis is a reminder that the sibling relationship warrants more attention in research as well as in clinical settings.
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