Abstract
Correlation between parents for a given characteristic substantively affects estimates of both genetic and environmental parameters. Spouse similarity for biological, adoptive, and nonadoptive parents was examined in a study using a full‐adoption design. With regard to isophormic comparisons, moderate assortment was found for age, educational attainment, performance on tests of verbal ability, family background, and habits such as alcohol and current smoking behavior. The effects of cross‐assortative mating on population covariance and cross‐correlation between relatives are discussed. Although of considerable theoretical interest, little cross‐trait assortative mating for personality and cognition was found in the present study, suggesting that its effects will not be large, at least for these variables. Because “assortative mating” may differ from “assortative marriage,” comparisons among estimates of homogamy for birth, adoptive, and nonadoptive parents were made. Results indicated differential assortment among the three types of parents for some of the variables examined.