Waller N G
Department of Psychology, University of California, Davis 95616.
Behav Genet. 1994 Mar;24(2):149-53. doi: 10.1007/BF01067818.
Parameter estimates from the DeFries and Fulker [(DF) Behav. Genet. 15:462-473, 1985] regression method can be greater than unity or less than zero. This occurs when the monozygotic correlation is greater than twice the dizygotic correlation. Sensible values can be obtained in these cases by fitting a constrained DF model that estimates genetic and nonshared environmental variance components only. In this article I demonstrate that the original Df model yields positively biased heritability estimates and negatively biased estimates of shared environmentality when data are significantly influenced by genetic nonadditivity. The magnitude of the bias is algebraically expressed. I then describe a simple regression equation that provides unbiased estimates of the standardized additive and dominance genetic variance components. Results of a study of 6 million twin pairs from the Monte Carlo Twin Registry demonstrate that the DF additive and dominance genetic parameter estimates are virtually identical to those obtained by maximum-likelihood procedures. Finally, I derive the expectations for the constrained DF model and show that the genetic parameter estimates from this model are negatively biased estimates of broad-sense heritability.
来自德弗里斯和富尔克（DeFries and Fulker）[(DF)《行为遗传学》（Behav. Genet.）15:462 - 473, 1985]回归方法的参数估计值可能大于1或小于0。当同卵双生子相关性大于异卵双生子相关性的两倍时，就会出现这种情况。在这些情况下，通过拟合仅估计遗传和非共享环境方差成分的受限DF模型，可以获得合理的值。在本文中，我证明了当数据受到遗传非加性的显著影响时，原始的DF模型会产生正偏差的遗传力估计值和负偏差的共享环境估计值。偏差的大小用代数形式表示。然后我描述了一个简单的回归方程，它能提供标准化加性和显性遗传方差成分的无偏差估计值。对来自蒙特卡洛双胞胎登记处的600万对双胞胎的研究结果表明，DF加性和显性遗传参数估计值与通过最大似然法获得的估计值几乎相同。最后，我推导了受限DF模型的期望值，并表明该模型的遗传参数估计值是广义遗传力的负偏差估计值。
