Parental Education and Child's Verbal IQ in Adoptive and Biological Families in the National Longitudinal Study of Adolescent Health

This study compared adoptive children and matched, biological children to estimate the genetic and environmental effect of years of mothers' and fathers' education on children's verbal intelligence (VIQ), as assessed by knowledge of vocabulary words. Adoptive and biological adolescent children in the National Longitudinal Study of Adolescent Health (Add Health) were matched for sex, age, parental education, and ethnicity. The adolescents all resided with two parents. Structural equation modeling was employed using Mx to estimate the genetic and transmissible environmental components of the correlation between parental education and children's VIQ. The mother-child and father-child correlations in biological families were .41 and .36, respectively, vs .16 and .18 in adoptive families. As suggested by these correlations, both genetic and shared environmental influences were statistically significant in the Mx models. We conclude that parental education exerts a modest shared environmental effect, explaining no more than 3 to 4% of the variation in verbal intelligence.