Pairs of same-sexed siblings discordant for antisocial behaviour.

Seventy-one pairs of same-sexed biological adolescent siblings, discordant for antisocial behaviour and service contact, were compared using matched-pairs analyses along several dimensions which included developmental, family, psychiatric, educational, cognitive, pro- and antisocial behaviour. The antisocial youth had significantly more negative perception and experiences than their siblings, who experienced more protective influences. Earlier onset in the antisocial youth of activities such as smoking also significantly differentiated the pairs. The early temperament index alone correctly classified as proband and sibling 95% of the youth, using discriminant analysis procedures. The findings are relevant to the aetiology of antisocial behaviour and to possible treatment interventions.