Personality factors in monozygotic and dizygotic twins: a comparative study.

To explore similarities or differences on a number of psychological variables relating to personality for members of 16 pairs of monozygotic and 16 pairs of dizygotic twins and between the two groups, the Rorschach, Luscher, Cattell 16 PF, Bem Sex-role Inventory, and Symptom Distress Check List were given to 64 subjects. Analysis confirms data in the literature concerning significant similarities on some personality traits for monozygotic and dizygotic pairs, but with some differences between the groups tested. The particular similarity between the twins may be more attributable to the type of relationship developed early between the twins and the mother than to a greater genetic than environmental influence.