Psychological medicine
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Psychological medicine · May 1998
Twin studies of adult psychiatric and substance dependence disorders: are they biased by differences in the environmental experiences of monozygotic and dizygotic twins in childhood and adolescence?
Twin studies have long been used to disentangle the role of genetic and environmental factors in the aetiology of psychiatric disorders. However, the validity of the twin method depends on the equal environment assumption--that monozygotic (MZ) and dizygotic (DZ) twins are equally correlated in their exposure to environmental factors of aetiological importance for the disorder under study. ⋯ Differential environmental experiences of MZ and DZ twins in childhood and adolescence are unlikely to represent a substantial bias in twin studies of most major psychiatric and substance dependence disorders but may influence twin similarity for the initiation of substance use.