Huang Jason Kunming, Tai John Jen
Department of Banking and Finance, Takming College, Taipei 114, Taiwan.
Stat Med. 2007 Feb 20;26(4):869-94. doi: 10.1002/sim.2573.
In human genetics, twin studies are widely underwent for investigation of the genetic influence on diseases. There are several measures that had been proposed to evaluate the similarity between two twins for dichotomous traits when the twins are sampled at random. These measures include the correlations, odds ratios, and casewise and pairwise concordances. When data are sampled through an ascertainment procedure, truncated data are formed. Under this circumstance, odds ratio cannot be defined and correlations cannot be correctly estimated. However, concordance measures for dichotomous traits can still be estimated using the likelihood method. On the other hand, though theoretically concordance measures can be extended to trichotomous traits, how to define them and to derive their estimators for ascertained trichotomous traits data have not been thoroughly discussed. In this study, we aim to address several relevant issues for ascertained trichotomous traits data. We define two new (casewise and pairwise) concordance measures for trichotomous traits and demonstrate how to apply a so-called 'self-contained subsets method (SCSM)' to estimation of twin concordances for ascertained data. We show that this method can obtain the same estimates as the likelihood method in an easier way and derive the asymptotic variances of the SCSM estimates under ascertainment. We establish the testing procedure for test of the equality of concordance measures between monozygotic twin pairs and dizygotic twin pairs, and illustrate the methods with a real data set and conduct Monte Carlo simulation to investigate its power performance.
在人类遗传学中，双胞胎研究被广泛用于调查疾病的遗传影响。当随机抽取双胞胎样本时，已经提出了几种方法来评估双胞胎在二分性状上的相似性。这些方法包括相关性、比值比以及逐例和成对一致性。当通过确定程序进行数据采样时，会形成截断数据。在这种情况下，无法定义比值比，也无法正确估计相关性。然而，对于二分性状的一致性测量仍可使用似然法进行估计。另一方面，尽管从理论上讲一致性测量可以扩展到三分性状，但对于已确定的三分性状数据，如何定义它们以及推导其估计量尚未得到充分讨论。在本研究中，我们旨在解决已确定的三分性状数据的几个相关问题。我们为三分性状定义了两个新的（逐例和成对）一致性测量，并展示了如何应用所谓的“自包含子集法（SCSM）”来估计已确定数据的双胞胎一致性。我们表明，该方法可以以更简单的方式获得与似然法相同的估计值，并推导在确定情况下SCSM估计值的渐近方差。我们建立了用于检验同卵双胞胎对和异卵双胞胎对之间一致性测量是否相等的检验程序，并用一个真实数据集说明了这些方法，并进行蒙特卡罗模拟以研究其功效表现。
