Although the demographic characteristics of the adoptive parents were more favorable than those of the birth parents (as in prior adoption studies; DeFries et al. 1994), a systematic test of range restriction biases has shown negligible effects on estimates of heritability and the environment, even when range restriction was present (McGue et al. 2007). Further, the differences between birth family and adoptive family characteristics suggest the unique utility of adoption as a preventive intervention focused on children's sociodemographic environments.
