Indirect vertical cultural transmission: a model for nongenetic parental influences on the liability to psychiatric illness.

A long tradition in psychiatry has focused on parental traits that directly influence the liability to psychiatric disorders in offspring. Because these traits rarely resemble the disorders they cause, traditional models of cultural transmission (which assume that "like perpetuates like") may not be appropriate. The author develops and illustrates several models for indirect vertical cultural transmission of psychiatric illness. These models generate falsifiable predictions about the pattern of risk in relatives of affected individuals. For example, all such models predict a substantially higher risk of illness in siblings than in offspring of affected individuals. It is now possible to develop and test rigorous models for the cultural transmission of psychiatric illness.