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Bias in variance components due to nonresponse in twin studies
Stockholm University, Faculty of Science, Department of Mathematics.
Stockholm University, Faculty of Science, Department of Mathematics.
2006 (English)In: Twin Research and Human Genetics, ISSN 1832-4274, Vol. 9, no 2, 185-193 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2006. Vol. 9, no 2, 185-193 p.
URN: urn:nbn:se:su:diva-25715OAI: diva2:200341
Part of urn:nbn:se:su:diva-848Available from: 2006-03-02 Created: 2006-03-02 Last updated: 2010-12-08Bibliographically approved
In thesis
1. Latent variable models for longitudinal twin data
Open this publication in new window or tab >>Latent variable models for longitudinal twin data
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Longitudinal twin data provide important information for exploring sources of variation in human traits. In statistical models for twin data, unobserved genetic and environmental factors influencing the trait are represented by latent variables. In this way, trait variation can be decomposed into genetic and environmental components. With repeated measurements on twins, latent variables can be used to describe individual trajectories, and the genetic and environmental variance components are assessed as functions of age. This thesis contributes to statistical methodology for analysing longitudinal twin data by (i) exploring the use of random change point models for modelling variance as a function of age, (ii) assessing how nonresponse in twin studies may affect estimates of genetic and environmental influences, and (iii) providing a method for hypothesis testing of genetic and environmental variance components. The random change point model, in contrast to linear and quadratic random effects models, is shown to be very flexible in capturing variability as a function of age. Approximate maximum likelihood inference through first-order linearization of the random change point model is contrasted with Bayesian inference based on Markov chain Monte Carlo simulation. In a set of simulations based on a twin model for informative nonresponse, it is demonstrated how the effect of nonresponse on estimates of genetic and environmental variance components depends on the underlying nonresponse mechanism. This thesis also reveals that the standard procedure for testing variance components is inadequate, since the null hypothesis places the variance components on the boundary of the parameter space. The asymptotic distribution of the likelihood ratio statistic for testing variance components in classical twin models is derived, resulting in a mixture of chi-square distributions. Statistical methodology is illustrated with applications to empirical data on cognitive function from a longitudinal twin study of aging.

Place, publisher, year, edition, pages
Stockholm: Matematiska institutionen, 2006. 49 p.
Latent variable models, twin models, variance components, change point models, non-ignorable nonresponse, likelihood ratio tests
National Category
Probability Theory and Statistics
urn:nbn:se:su:diva-848 (URN)91-7155-211-1 (ISBN)
Public defence
2006-03-24, sal 14, hus 5, Kräftriket, Stockholm, 10:00
Available from: 2006-03-02 Created: 2006-03-02Bibliographically approved

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