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The equal environments assumption of classical twin studies may not hold

Richardson, K and Norgate, SH 2005, 'The equal environments assumption of classical twin studies may not hold' , British Journal of Educational Psychology, 75 (3) , pp. 339-350.

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        Abstract

        The classical twin method – comprising comparisons of monozygotic (MZ) and dizygotic (DZ) twins – in the domain of cognitive abilities and attainments has led to wide acceptance of results suggesting a large amount of additive genetic variance, with far-reaching implications both for the nature of future studies on the causes of cognitive variance and for intervention policies, as in education. However, this interpretation is only valid if the method observes a number of conditions, which have to hold. Here, we show that the most crucial of these, namely, the equal environments assumption (EEA), may not hold. Consequently, differences in twin correlations might be at least partly explained by treatment effects from parents, teachers, peers, and so on. In addition, well-known interactions at various levels confound the model of simple additive effects on which the classical twin method is predicated and results are interpreted. For example, at a socio-cognitive level, DZ twins may respond to treatments differently from MZ twins. This interaction may further explain MZ–DZ correlation differences. There is abundant evidence for such interactive effects in published twin data. We suggest that there is a need for a more thorough examination of these problems.

        Item Type: Article
        Themes: Subjects / Themes > H Social Sciences > HQ The family. Marriage. Woman > HQ503 The family. Marriage. Home > HQ0767 Children. Child development
        Subjects / Themes > R Medicine > R Medicine (General)
        Health and Wellbeing
        Subjects outside of the University Themes
        Schools: Colleges and Schools > College of Health & Social Care > School of Health Sciences > Centre for Health Sciences Research
        Colleges and Schools > College of Health & Social Care
        Colleges and Schools > College of Health & Social Care > School of Nursing, Midwifery, Social Work & Social Sciences > Centre for Social Justice Research
        Journal or Publication Title: British Journal of Educational Psychology
        Publisher: British Psychological Society
        Refereed: Yes
        ISSN: 00070998
        Depositing User: H Kenna
        Date Deposited: 03 Aug 2007 11:33
        Last Modified: 20 Aug 2013 16:45
        URI: http://usir.salford.ac.uk/id/eprint/93

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