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Bias in variance components due to nonresponse in twin studies
Annica Dominicus1, Juni Palmgren, Nancy L Pedersen
1Department of Mathematics, Stockholm University, Stockholm, Sweden. annicad@math.su.se
Summary
Missing data in twin studies can skew genetic and environmental variance estimates. Our findings suggest that declining genetic influences on cognitive abilities with age are real, not just due to participant dropout.
Area of Science:
- Behavioral Genetics
- Biostatistics
- Gerontology
Background:
- Incomplete data in twin analyses can lead to biased estimates of genetic and environmental variance components.
- The ignitability of nonresponse mechanisms is crucial for consistent variance component estimation using methods like full information maximum likelihood.
- Non-ignorable nonresponse mechanisms complicate variance component estimation in twin studies.
Purpose of the Study:
- To investigate the impact of nonresponse mechanisms on genetic and environmental variance estimates in twin studies.
- To assess potential bias in variance component estimates due to different nonresponse mechanisms using Monte Carlo simulations.
- To interpret findings from the Swedish Adoption/Twin Study of Aging regarding cognitive abilities in late life.
Main Methods:
- Monte Carlo simulation to assess bias in variance component estimates under various nonresponse scenarios.
- Analysis of nonresponse correlation within monozygotic (MZ) and dizygotic (DZ) twin pairs.
- Application of simulation results to interpret longitudinal data on perceptual speed.
Main Results:
- Within-pair nonresponse correlation, potentially differing between MZ and DZ twins, can be compatible with ignorable nonresponse.
- Simulation results provide guidance on interpreting variance component estimates affected by nonresponse.
- The observed decrease in genetic influences on perceptual speed over 13 years is unlikely to be solely due to study attrition.
Conclusions:
- The observed decline in genetic influences on perceptual speed in late life is a genuine phenomenon.
- This finding supports the hypothesis that genetic contributions to certain cognitive abilities diminish with advancing age.
- Careful consideration of nonresponse mechanisms is essential for accurate genetic analyses in longitudinal twin studies.
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