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The “Equal Environments Assumption” in MZ-DZ Twin Comparisons: an Untenable Premise of Psychiatric Genetics?

Published online by Cambridge University Press:  01 August 2014

A. Pam ,
S.S. Kemker ,
C.A. Ross  and
R. Golden
A. Pam*
Affiliation:
Albert Einstein College of Medicine, Bronx, New York
S.S. Kemker
Affiliation:
Albert Einstein College of Medicine, Bronx, New York
C.A. Ross
Affiliation:
Dissociative Disorders Unit, Charter Hospital of Dallas Richardson, Texas, USA
R. Golden
Affiliation:
Albert Einstein College of Medicine, Bronx, New York
*
Director of Psychology, Bronx Psychiatric Center, 1500 Waters Place, Bronx, New York 10461, USA

Abstract

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The comparison of MZ-DZ twins in behavioral genetics has produced what seems like irrefutable evidence for the heritability of many psychiatric disorders. But such research depends on the validity of the EEA – the “equal environments assumption” – as an underlying premise. In this paper, several empirical studies which support the EEA are critically reviewed in terms of methodology and the way data has been processed in a mathematical model called “path analysis”. It turns out that studies investigating the EEA appear to be largely inadequate in terms of technique, as well as biased in the inferences drawn. Further, the “heritability” estimate – often taken to mean the influence of trait – specific genes – is merely a statistical abstraction derived from a matrix of correlations; this estimate encompasses many buried environmental effects so that “heritability” does not correspond to any underlying DNA structure. In conclusion, many MZ-DZ pedigree studies have dubious scientific value, given the non-viable premise of the EEA, as well as the misleading operational definition of what has been called “heritability”.

Type
Research Article
Information
Acta geneticae medicae et gemellologiae: twin research , Volume 45 , Issue 3 , July 1996 , pp. 349 - 360
Copyright
Copyright © The International Society for Twin Studies 1996

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