The development of psychopathic traits from childhood to adolescence

Previous research has shown that genetic factors are important in the stability of psychopathic personality from ages 17–24 years (D. M. Blonigen, B. M. Hicks, R. F. Krueger, C. J. Patrick, W. G. Iacono, 2006, Journal of Abnormal Psychology, 85–95) and ages 16–19 years (M. Forsman, P. Lichtenstein, H. Andershed, H. Larsson, 2008, Journal of Abnormal Psychology, 606–17). However, these studies did not examine the developmental trajectory of psychopathy, and they only evaluated psychopathy at two time points. The present study examined to what extent genetic and environmental effects influence initial level and change in psychopathic personality measured on three time. The USC Twin Study of Risk Factors for Antisocial Behavior is a longitudinal study of >600 twin pairs born 1990–1996 (L. A. Baker, M. Barton, D. I. Lozano, A. Raine, J. H. Fowler, 2006, Twin Research, 933–40). Psychopathic personality in the twins were assessed with the Child Psychopathy Scale (D. R. Lynam, 1997, Journal of Abnormal Psychology, 425–38) which was administered in interview format to the twins and their caregivers when the twins were aged 9–10 years, 11–14 years and 15–18 years old: N= 1,441 twins. Phenotypic Latent Growth Curve models were fit in MPlus (L. K. Muthén & B. O. Muthén, 1998–2007, Los Angeles, CA). Age variation within each wave of assessment is a powerful design for examining genetic and environmental influences on level and change (J. J. McArdle, 2006, Twin Research, 343–59) and was fit using Proc Mixed (SAS Institute, 2005). For both parent and self-report ratings of psychopathic traits, the best-fitting phenotypic growth model was a linear model, indicating significant growth in psychopathic traits, decreasing over time on average in parent reported ratings and increasing over time in youth selfreported ratings. For parent reports, slope variation was significant, suggesting that individuals have different trajectories. For youth-self-reports the slope variation was