Abstract
Despite an abundance of stereotypes about the power of sibling constellation factors, and clinicians expressed interest in the part siblings play in children s adjustment, the contribution of siblings to children s development of aggression has been a relatively neglected topic of research. The current study explores whether differences in structural features of the sibling constellation; the number, birth order, age spacing and gender of siblings, are related to differences in four-year-old children s levels of aggression. To inform such explorations, a diverse and disorganized literature on siblings, and findings from research on childhood developmental trajectories of aggression, are reviewed. The current study utilizes pre-collected data from a population-based longitudinal study, the Behavior Outlook Norwegian Developmental Study (BONDS), provided by The Norwegian Center for Child Behavioral Development. The BONDS sample included data from 1159 children recruited in three waves, in 2006-2008. Parental interviews where administered when target children were 0.5, 1, 2, 3 and 4 years old. The current study utilizes a subsample of 741 children and data from personal interviews with mothers (including a parent-completed questionnaire) when target children where 0.5 and 4 years old. At the 4 year interview, items from a physical aggression scale designed for the BONDS, and items from the aggressive behavior syndrome scale of the Child Behavior checklist VII for ages 1 ½ - 5 years, where used to obtain estimates of children s levels of aggression. Sibling constellation characteristics where recorded at both interviews. Potential covariates where obtained at the 6 month interview. MANOVA was performed for each of the three predictor variables; number of siblings, birth order and age spacing and sibling gender, to investigate their relationship with the two dependent variables physical aggression and aggressive behavior. ANOVA with post hoc tests were performed for statistically significant variables, and a hierarchical multiple regression analysis was performed to control for covariates. Results suggest, that on average, mother s reported low levels of physical aggression and aggressive behaviors. In contrast to popular stereotypes on birth order effects, after controlling for possible covariates, the presence of siblings, rather than constellation factors, was associated with slightly higher levels of physical aggression in target children. Such differences where not found for the aggressive behavior syndrome scale (CBCL), highlighting the importance of comparing measures of aggression.