Nonshared experiences within the family: Correlates of behavioral problems in middle childhood

Abstract

AbstractOne of the most dramatic findings from quantitative genetic research is that environmental influences shared by siblings in a family do not make the siblings similar in terms of psychopathology. Sibling resemblance for psychopathology appears to be genetic rather than environmental in origin; environmental influences that affect the development of psychopathology must be nonshared and make children in the same family different rather than similar. This study sets out to identify environmental factors that differ for young siblings and to assess associations between such nonshared factors and differences in the older siblings' outcome in two domains: internalizing and externalizing behavior problems. Maternal interview and observations of differential maternal and sibling behavior were compared within 67 sibling dyads (younger and older siblings aged 4 and 7 years, respectively, on average), and differential experiences were related to the adjustment of the older sibling, as assessed by mother and teacher. Differential maternal behavior appeared to be particularly important as a predictor of adjustment problems. Older siblings showed internalizing problems in families in which mothers were less affectionate to the older than to the younger sibling. Greater maternal control toward the older than the younger sibling predicted both internalizing and externalizing problems. Differential maternal behavior explained 34% of the variance of internalizing behavior and 27% of the variance of externalizing behavior problems, independent of variance explained by family structure variables. Although the sample was unselected for psychopathology and was too small to permit analyses of the diagnosable extremes of internalizing and externalizing dimensions, these results are encouraging in relation to the goal of identifying systematic sources of nonshared environment that affect the development of psychopathology.