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Bias in Variance Components Due to Nonresponse in Twin Studies

Published online by Cambridge University Press:  21 February 2012

Annica Dominicus ,
Juni Palmgren  and
Nancy L. Pedersen
Annica Dominicus*
Affiliation:
Department of Mathematics, Stockholm University, Stockholm, Sweden; Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden. annicad@math.su.se
Juni Palmgren
Affiliation:
Department of Mathematics, Stockholm University, Stockholm, Sweden; Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
Nancy L. Pedersen
Affiliation:
Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden; Department of Psychology, University of Southern California, Los Angeles, United States of America.
*
*Address for correspondence: Annica Dominicus, Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Box 281, SE-171 77 Stockholm, Sweden.

Abstract

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Incomplete data on trait values may bias estimates of genetic and environmental variance components obtained from twin analyses. If the nonresponse mechanism is ‘ignorable’ then methods such as full information maximum likelihood estimation will produce consistent variance component estimates. If, however, nonresponse is ‘nonignorable’, then the situation is more complicated. We demonstrate that a within-pair correlation of nonresponse, possibly different for monozygotic (MZ) and dizygotic (DZ) twins, may well be compatible with ‘ignorability’. By means of Monte Carlo simulation, we assess the potential bias in variance component estimates for different types of nonresponse mechanisms. The simulation results guide the interpretation of analyses of data on perceptual speed from the Swedish Adoption/Twin Study of Aging. The results suggest that the dramatic decrease in genetic influences on perceptual speed observed after 13 years of follow-up is not attributable solely to dropout from the study, and thus support the hypothesis that genetic influences on some cognitive abilities decrease with age in late life.

Type
Articles
Information
Twin Research and Human Genetics , Volume 9 , Issue 2 , 01 April 2006 , pp. 185 - 193
Copyright
Copyright © Cambridge University Press 2006