Lea Pulkkinen1, Jaakko Kaprio2,3, & Richard J. Rose4
The Multidimensional Peer Nomination Inventory (MPNI; 30 items), and its parallel teacher- and parental-rating forms (37 items each), were developed and administered to 944 12 year-old Finnish twins drawn from three nation-wide birth cohorts (1983-85) in an ongoing, longitudinal study, FinnTwin12. A total of 12,937 children participated in peer nominations in the 503 school classes in which the targeted twins were enrolled. The twins formed 154 MZ, 132 same-sex DZ, and 127 opposite-sex DZ pairs with complete data and confirmed zygosity. Data from peer nominations, teacher- and parental- ratings, yielded three factors, with scales (and subscales) for Behavioral Problems (Hyperactivity-Impulsivity, Aggression, Inattention), Emotional Problems (Depression, Social Anxiety), and Adjustment (Constructiveness, Compliance, Social Activity). Results from the 944 twin individuals provide evidence of reliability and concurrent validity (against teacher ratings) of peer-referenced assessment, and all scales, except Depression and Social Anxiety, differentiated boys from girls in expected directions. Consistently, across scales and across informants, correlations for MZ cotwins exceeded those for DZ cotwins, but, across informants, significant similarity was found for both SSDZ and OSDZ twins, as well, with little evidence of contrast effects. In peer nominations, all MZ correlations were 0.70 or higher, and DZ correlations ranged from 0.29 to 0.53. The pattern of twins' correlations suggests substantial additive genetic variance in all scales of the MPNI with no effects of sex-limitation at this age; modeling, with Mx, will be used to confirm these suggestions, when subject ascertainment is complete and the twin sample is doubled in size.
Address: Department of Psychology, University of Jyväskylä, P.O.Box 40351, Jyväskylä, Finland; email, leapulkk@tukki.jyu.fi
1Department of Psychology, University of Jyväskylä 2Department of Mental Health and Alcohol Research, National Public Health Institute, Helsinki 3Department of Public Health, University of Helsinki 4Department of Psychology, Indiana University, Bloomington 5FinnTwin12 is supported by AA-09203 and the Academy of Finland