A monozygotic twin differences study of nonshared environmental influence on adolescent depressive symptoms.

The monozygotic (MZ) twin differences method was used to examine nonshared environmental aspects of the association of parenting (punitive and constructive discipline), negative life events (independent and dependent), and peers (antisocial and prosocial) with adolescent depressive symptoms in terms of sequelae, risk, and maintaining factors. Two self-report booklets were completed by 328 MZ twin pairs aged 12-19 years, 6 months apart. Increased punitive discipline and negative life events were found to be relevant nonshared environmental factors that followed depression. Negative life events were the only factor that had a direct nonshared environmental association with concurrent depressive symptoms in adolescents independent of previous depressive symptoms, and all other study variables.