Gottesman and Shields
The aim of the study was to review research on family, twin and adoption studies to test for evidence of a genetic cause of Schizophrenia.
The participants were 711 participants of adoption studies, 210 monozygotic twins and 316 dizygotic twins studied.
The method was a review article of 3 adoption and 5 twin studies between 1967 and 1976.
The procedure looked at the concordance rates (how often both twins were diagnosed with Schizophrenia), and incidence of Schizophrenia in parents and children in biological and adoptive families.
All 3 adoption studies showed increased incidence of Schizophrenia in adopted children with a Schizophrenic biological parent, but normal children fostered with a Schizophrenic adoptive parent did not develop Schizophrenia.
The twin studies also supported the biological explanation, with monozygotic twins showing a 58% concordance rate compared to 12% in dizygotic twins.