An international panel of seven diagnosticians from Japan, Sweden, the United Kingdom, and the United States blindly diagnosed the histories of the 114 twins in the Maudsley schizophrenic twin series. The middle-of-the-road consensus diagnosis of schizophrenia was easily reached. Besides being more reliable, it gave better monozygotic to dizygotic (MZ:DZ) discrimination than attempts to apply broader or narrower diagnostic criteria. A similar standard applied to the other recent schizophrenic twin studies secured reasonable agreement, and the pooled MZ concordance rate from the studies was 46%, higher than sometimes reported. The study vindicates both the diagnosis of schizophrenia and its substantial heritability.
Shields J, Gottesman II. Cross-National Diagnosis of Schizophrenia in TwinsThe Heritability and Specificity of Schizophrenia. Arch Gen Psychiatry. 1972;27(6):725-730. doi:10.1001/archpsyc.1972.01750300005001