Derks Eske M, Dolan Conor V, Boomsma Dorret I
Department of Biological Psychology, Vrije Universiteit, Amsterdam, the Netherlands.
Twin Res Hum Genet. 2006 Jun;9(3):403-11. doi: 10.1375/183242706777591290.
In the classic twin design, estimation of genetic and environmental effects is based on the assumption that environmental influences are shared to the same extent by monozygotic and dizygotic twins (equal environment assumption, EEA). We explore the conditions in which the EEA can be tested based on multivariate phenotypic data. We focus on the test whether the correlation between shared environmental factors in dizygotic twins (r(C)) is less than 1. First, model identification was investigated analytically in Maple and Mx. Second, statistical power was examined in Mx. Third, the amount of bias caused by violation of the EEA was evaluated. Finally, applications to empirical data concern spatial ability in adolescents and aggression in children. Bivariate and trivariate models include several instances in which the EEA can be tested. The number of twin pairs that is needed to detect violation of the EEA with a statistical power of .80 (alpha = .05) varied between 508 and 3576 pairs for the situations considered. The bias in parameter estimates, given misspecification, ranged from 5% to 34% for additive genetic effects, and from 4% to 34% for shared environmental effects. Estimates of the nonshared environmental effects were not biased. The EEA was not violated for spatial ability or aggression. Multivariate data provide sufficient information to test the validity of the EEA. The number of twin pairs that is needed is no greater than the number typically available in most twin registries. The analysis of spatial ability and aggression indicated no detectable violation of the EEA.
在经典双胞胎设计中，对遗传和环境效应的估计基于这样一个假设：同卵双胞胎和异卵双胞胎受到环境影响的程度相同（等环境假设，EEA）。我们探讨了基于多变量表型数据检验EEA的条件。我们重点关注检验异卵双胞胎中共享环境因素之间的相关性（r(C)）是否小于1。首先，在Maple和Mx中进行了分析性的模型识别。其次，在Mx中检验了统计功效。第三，评估了违反EEA所导致的偏差量。最后，将其应用于青少年空间能力和儿童攻击性的实证数据。双变量和三变量模型包括了几个可以检验EEA的实例。在所考虑的情况下，要以0.80的统计功效（α = 0.05）检测到EEA被违反所需的双胞胎对数在508对至3576对之间变化。给定错误设定时，加性遗传效应的参数估计偏差范围为5%至34%，共享环境效应的偏差范围为4%至34%。非共享环境效应的估计没有偏差。空间能力或攻击性方面未违反EEA。多变量数据为检验EEA的有效性提供了足够的信息。所需的双胞胎对数不超过大多数双胞胎登记处通常可获得的数量。对空间能力和攻击性的分析表明未检测到违反EEA的情况。
