Affective illness in family members and matched controls.

As part of the US National Institute of Mental Health Collaborative Program on the Psychobiology of Depression study, a subset of 460 randomly chosen relatives of affectively ill probands were compared to a control group matched by the acquaintanceship method. The rate of major affective disorder in relatives was found to be 36%; the rate among controls was 28%. Relatives were also found to have significantly higher rates of bipolar II disorder, any Research Diagnostic Criteria (RDC) affective disorder and any RDC mental disorder. All of these rates were found to be significantly higher when female relatives were compared with their acquaintances, but only the rate of any RDC mental disorder was higher when this comparison was made in men. The acquaintanceship method enabled the selection of a control group that closely resembled the relatives, probably to the extent of "overmatching". When the match was evaluated to determine whether relatives tended to select comparably ill (or well) acquaintances, this was found to be the case only for alcoholic and never mentally ill relatives.