Table 3.

Power calculations for this study, if we assume the test marker is in perfect linkage disequilibrium with the true causative locus.^a

A: where α = 0.05 (without correction for multiple-testing)
H2	TDT	Case-control
0.02	0.121	0.464
0.05	0.231	0.849
0.10	0.403	0.989
0.20	0.669	1.000
B: where α = 0.001 (with correction for multiple-testing)
H2	TDT	Case-control
0.02	0.006	0.078
0.05	0.019	0.383
0.10	0.058	0.836
0.20	0.186	0.997

TDT, transmission disequilibrium test.

^aThe optimal situation is calculated with a K = 0.20 (incidence of nonallergic vasomotor rhinitis in the United States is estimated to be between 20% and 25%) and the minor allele frequency = 0.1. H² denotes heritability (the proportion of phenotypic variation ascribed to the genetic variability at the putative locus under investigation). The reason for including an H² of 0.10 and 0.20 is to attain “the highest achievable” statistical power for our small-sample TDT analysis—although such high heritability levels seldom occur in common diseases. Additivity is assumed in these power calculations. These calculations underscore the fact that the power of the TDT analysis is far lower than that of the case-control study.