Analytic power and sample size calculation for the genotypic transmission/disequilibrium test in case‐parent trio studies

Case-parent trio studies considering genotype data from children affected by a disease and from their parents are frequently used to detect single nucleotide polymorphisms (SNPs) associated with disease. The most popular statistical tests in this study design are transmission/disequlibrium tests (TDTs). Several types of these tests have been developed, e.g., procedures based on alleles or genotypes. Therefore, it is of great interest to examine which of these tests have the highest statistical power to detect SNPs associated with disease. Comparisons of the allelic and the genotypic TDT for individual SNPs have so far been conducted based on simulation studies, since the test statistic of the genotypic TDT was determined numerically. Recently, it, however, has been shown that this test statistic can be presented in closed form. In this article, we employ this analytic solution to derive equations for calculating the statistical power and the required sample size for different types of the genotypic TDT. The power of this test is then compared with the one of the corresponding score test assuming the same mode of inheritance as well as the allelic TDT based on a multiplicative mode of inheritance, which is equivalent to the score test assuming an additive mode of inheritance. This is, thus, the first time that the power of these tests are compared based on equations, yielding instant results and omitting the need for time-consuming simulation studies. This comparison reveals that the tests have almost the same power, with the score test being slightly more powerful.