A test of the equal-environment assumption in twin studies of psychiatric illness
- 1 January 1993
- journal article
- research article
- Published by Springer Science and Business Media LLC in Behavior Genetics
- Vol. 23 (1), 21-27
- https://doi.org/10.1007/bf01067551
Abstract
The traditional twin method is predicated on the equal-environment assumption (EEA)—that monozygotic (MZ) and dizygotic (DZ) twins are equally correlated in their exposure to environmental events of etiologic importance for the trait under study. In 1968, Scarr proposed a test of the EEA which examines the impact of phenotypic similarity in twins of perceived versus true zygosity. We apply this test for the EEA to five common psychiatric disorders (major depression, generalized anxiety disorder, phobia, bulimia, and alcoholism), as assessed by personal interview, in 1030 female-female twin pairs from the Virginia Twin Registry with known zygosity. We use a newly developed model-fitting approach which treats perceived zygosity as a form of specified familial environment. In 158 of the 1030 pairs (15.3%), one or both twins disagreed with the project-assigned zygosity. Model fitting provided no evidence for a significant influence of perceived zygosity on twin resemblance for any of the five disorders. Although limited in power, these results support the validity of the EEA in twin studies of psychiatric disorders.Keywords
This publication has 27 references indexed in Scilit:
- Social contact and sibling similarity: Facts, issues, and red herringsBehavior Genetics, 1990
- Does contact lead to similarity or similarity to contact?Behavior Genetics, 1990
- Twins: a test of the equal environments assumptionActa Psychiatrica Scandinavica, 1990
- Change in cohabitation and intrapair similarity of monozygotic (MZ) cotwins for alcohol use, extraversion, and neuroticismBehavior Genetics, 1990
- A Twin Study of Hyperactivity—II. The Aetiological Role of Genes, Family Relationships and Perinatal AdversityJournal of Child Psychology and Psychiatry, 1989
- Twin method: Defense of a critical assumptionBehavior Genetics, 1979
- Do parents create, or respond to, differences in twins?Developmental Psychology, 1977
- Relations between twins' similarity of appearance and behavioral similarity: Testing an assumptionBehavior Genetics, 1976
- The Syntactic Abilities of Identical Twins, Fraternal Twins, and Their SiblingsChild Development, 1976
- Resemblance in appearance and the equal environments assumption in twin studies of personality traitsBehavior Genetics, 1976