Beyond nature versus nurture: DF analysis of nonshared influences on problem behaviors.

J. C. DeFries and D. W. Fulker's (1985) regression model (since named DF analysis) used kinship pair data to separate heredity and shared environmental influences. This article extends DF analysis to include measured indicators of the nonshared environment. These indicators represent specific sources of environmental influence that cause related children to be different from one another. We present two empirical studies using twin, full-sibling, half-sibling, and cousin pairs from over 7,000 5- to 11-year-old children in the National Longitudinal Survey of Youth. Study 1 is a validity analysis of kinship height and weight data. Study 2 is a DF analysis of problem behavior scores