Quality of parent-child relationships was assessed using the Parental Environment Questionnaire (PEQ), a 50-item self-report questionnaire that assesses multiple dimensions of the parent-child relationship (e.g., conflict, involvement; scale α's range from .82 to .69)50,51. Twins completed separate PEQ ratings regarding their relationship with their mother and father. Parents also rated their relationship with each twin as well as the quality of the relationship between each twin and the other parent (e.g., mother rated the relationship between each twin and their father). Therefore, up to 3 ratings were available for the mother-child and father-child relationship. The measure of mother-child and father-child relationship problems used in the analyses was the mean of the 3 informant ratings on the first principal component among the PEQ scales (the scales exhibit a dominant 1st component; mean correlation across informants was .41).
