Effects on sibship size and composition on younger brothers' and sisters' alcohol use initiation: findings from an Australian twin sample
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The effects of sibship size and structure on delinquency are well established, but despite strong links between delinquency and alcohol use, the contribution of these factors to drinking behaviors remains largely unexplored. The current study investigated the impact of sibship size and composition on younger brothers' and sisters' ages of drinking and intoxication onset. Large sibship size was hypothesized to facilitate earlier onset in both males and females, and having many older brothers was hypothesized to predict earlier drinking in males and later drinking in females. These hypotheses were tested through a series of statistical investigations performed on information collected from a large Australian twin sample. Results indicated that sibship size and composition effects are strongest when older siblings are close in age. In addition, close in age siblings exerted the strongest effects on drinking when: (1) respondents were from homes of divorce; and (2) they did not have a paternal history of alcohol problems. Potential mechanisms behind these effects and their implications for prevention and intervention are discussed.