Abstract
Results from analyses of twin data that use models assuming a bivariate distribution of twin values will change when twins within pairs are reordered. We examined the effect of twin pair ordering on additive genetic variance estimates and hypothesis tests, from a bivariate normal model, both via simulation and through examination of real twin data. The simulations generated twin data for varying sample sizes and amounts of additive genetic and common environmental variance. The real data sets had sample sizes of 60 or less per zygosity. The results indicate that for moderate or large size studies, the effects of twin pair ordering are unlikely to greatly change the results of the data analysis; but for small studies the results can be sensitive to twin pair ordering. We therefore suggest that methods, not sensitive to within twin-pair differences be compared to the results obtained from twin-pair ordering. Methods not influenced by twin-pair ordering include least squares methods or covariance matrices approaches as described by Carey (2005, Behav Genet 35:667–670) or Guo and Wang (2002, Behav Genet 32:37–49).
References
Aptech Systems Inc. 1993. GAUSS, Maple Valley, WA, http://www.aptech.com
Carey G (2005) The intraclass covariance matrix. Behav Genet 35:667–670
Guo G, Wang J (2002) The mixed or multilevel model for behavior genetic analysis. Behav Genet 32:37–49
Neale MC, Cardon LR (1992) Methodology for genetic studies of twins and families. Kluwer, Dordrecht
R: Development Core Team 2004. R: a language and environment for statistical computing. R Foundation for Statistical Computing. Vienna, Austria. http://www.r-project.org
SAS Institute Inc. 2004 SAS® 9.1.3 Language Reference: Concepts. SAS Institute Inc., Cary, NC, USA. http://www.sas.com
Sokol DK., Moore CA, Rose RJ, Williams CJ, Reed TE, Christian JC (1995) Intra-pair differences in personality and cognitive ability among young monozygotic twins distinguished by chorion type. Behav Genet 25(5):657–664
Author information
Authors and Affiliations
Corresponding author
Additional information
Edited by Stacey Cherny
Rights and permissions
About this article
Cite this article
Byrne, E., Stillitano, M., Williams, C.J. et al. The Influence of Twin Pair Permutation on Likelihood-Based-Estimates of Genetic Variance That Require Ordering of Twin-Pairs. Behav Genet 37, 617–620 (2007). https://doi.org/10.1007/s10519-007-9154-3
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10519-007-9154-3