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November 1970

Schizophrenia in the NAS-NRC Panel of 15,909 Veteran Twin Pairs

Author Affiliations

Bethesda, Md
From the Section on Twin and Sibling Studies, Adult Psychiatrv Branch, National Institute of Mental Health, Bethesda, Md. Dr. Hoffer is now at the Massachusetts Mental Health Center, Boston.

Arch Gen Psychiatry. 1970;23(5):469-477. doi:10.1001/archpsyc.1970.01750050085012

THE CLASSICAL twin method has played a major role in influencing the direction of psychiatric thought on the relative importance of heredity and environment in the pathogenesis of schizophrenia. Fundamentally, this method is a comparison of a group of monozygotic or "identical" twins with a group of dizygotic or "fraternal" twins. The percentage of pairs where both twins are affected by a particular disease is compared in the two groups. This percentage is called the pairwise concordance rate. Since monozygotic twins are assumed to be genetically identical, while dizygotic twins no more so than nontwin siblings, comparisons of concordance rates between these two groups have been used to estimate the genetic contribution to a given illness.

In the past, studies showing a high concordance rate for schizophrenia in monozygotic twins and a much lower one in dizygotic twins have been accepted as

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