would already be influential for parental knowledge later on. We included information on and mental health in our analyses because parental family’s socioeconomic status parents’ monitoring, knowledge and antisocial behavior not only influence each other but may youths’ also be affected by other family characteristics that could explain the associations. We also considered different sources of information, including mothers, youths themselves, fathers and teachers, to test whether results were similar across informants. Finally, we tested for the presence of sex differences in the levels of parental knowledge and monitoring and in their longitudinal associations with antisocial behavior. Methods Sample Participants were members of the Environmental Risk (E-Risk) Longitudinal Twin Study, which tracks the development of a birth cohort of 2,232 British children. The sample was drawn from a larger birth register of twins born in England and Wales in 1994-95 (Trouton, Spinath, & Plomin, 2002). Full details about the sample are reported elsewhere (Moffitt & E-Risk Study Team, 2002). Briefly, the E-Risk sample was constructed in 2000, when 1116 families (93% of those eligible) with same-sex 5-year-old twins participated in home-visit assessments. The sample comprised 55% monozygotic (MZ) and 45% dizygotic (DZ) twin pairs; sex was evenly distributed within zygosity (49% male). Families were recruited to represent the UK population of families with newborns in the 1990s, on the basis of residential location throughout England and Wales and mother’s age. Teenaged mothers with twins were over-selected to replace high-risk families who were selectively lost to the register through non-response. Older mothers having twins via assisted reproduction were under-selected to avoid an excess of well-educated older mothers. The
would already be influential for parental knowledge later on. We included information on family’s socioeconomic status and parents’ mental health in our analyses because parental monitoring, knowledge and youths’ antisocial behavior not only influence each other but may also be affected by other family characteristics that could explain the associations. We also considered different sources of information, including mothers, youths themselves, fathers and teachers, to test whether results were similar across informants. Finally, we tested for the presence of sex differences in the levels of parental knowledge and monitoring and in their longitudinal associations with antisocial behavior. Methods Sample Participants were members of the Environmental Risk (E-Risk) Longitudinal Twin Study, which tracks the development of a birth cohort of 2,232 British children. The sample was drawn from a larger birth register of twins born in England and Wales in 1994-95 (Trouton, Spinath, & Plomin, 2002). Full details about the sample are reported elsewhere (Moffitt & E-Risk Study Team, 2002). Briefly, the E-Risk sample was constructed in when 1116 families (93% of those eligible) with same-sex 5-year-old twins participated in home-visit assessments. The sample comprised 55% monozygotic (MZ) and 45% dizygotic (DZ) twin pairs; sex was evenly distributed within zygosity (49% male). Families were recruited to represent the UK population of families with newborns in the 1990s, on the basis of residential location throughout England and Wales and mother’s age. Teenaged mothers with twins were over-selected to replace high-risk families who were selectively lost to the register through non-response. Older mothers having twins via assisted reproduction were under-selected to avoid an excess of well-educated older mothers. The 2000,