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Parent ratings of temperament in twins: explaining the ‘too low’ DZ correlations

Published online by Cambridge University Press:  21 February 2012

Kimberly J Saudino ,
Stacey S Cherny  and
Robert Plomin
Kimberly J Saudino*
Affiliation:
Psychology Department, Boston University, USA. [email protected]
Stacey S Cherny
Affiliation:
Wellcome Trust Centre for Human Genetics, University of Oxford, UK.
Robert Plomin
Affiliation:
Institute of Psychiatry, University of London, UK.
*
*Correspondence: Kimberly J Saudino, Psychology Department, Boston University, 64 Cummington St, Boston, MA 02215, USA. Tel: 617 353 3679; Fax: 617 353 6933

Abstract

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Twin studies of child temperament using objective measures consistently suggest moderate heritability for most dimensions. However, parent rating measures produce unusual patterns of results. Intraclass correlations for identical (MZ) twins are typically high, whereas fraternal (DZ) twin intraclass correlations are much lower than would be predicted from an additive genetic model. The ‘too low’ DZ correlations can be explained by parent-rating biases that either exaggerate the differences between DZ twins (contrast effects) or that inflate the similarity of MZ twins (assimilation effects), or by the presence of non-additive genetic variance. To evaluate the three possible explanations, we used model-fitting procedures applied to parent-rating data averaged across 14, 20, 24, and 36 months of age in a sample of 196 twin pairs participating in the MacArthur Longitudinal Twin Study. The data were best described by a model that included contrast effects. Implications for non-twin research are discussed. Twin Research (2000) 3, 224–233.

Keywords

twinstemperamentgeneticsrater biasmodel fitting
Type
Articles
Information
Twin Research and Human Genetics , Volume 3 , Issue 4 , 01 August 2000 , pp. 224 - 233
Copyright
Copyright © Cambridge University Press 2000