Bias against genetic hypotheses in adoption studies.

Genetic factors are implicated in the cause of psychopathological disorders whenever the incidence of disorder is greater among the adopted-away offspring of affected parents than among those of control (unaffected) parents. The lack of information about most parents who give their children up for adoption could result in the inclusion of a substantial number of high-risk parents in the control groups. This could bias an adoption study against a genetic hypothesis. The Minnesota Multiphasic Personality inventory scores of two groups of pregnant unwed mothers were compared to those of two other groups: married pregnant women and 18-year-old women. Comparisons disclosed that the unwed mothers had significant elevations on five to the nine clinical scales. Elevations on psychopathic deviancy and schizophrenia were particularly substantial. These results indicate a requirement to select control group parents who are representative of the general population.