Power loss (PL) for genetic association as a function of errorless power threshold and error probability ε. In this figure, we compute statistical power for the χ² test of independence on 2 × 3 contingency tables in the presence of genotype errors. Power is computed as a function of power without errors (2 settings for power used: 99% and 80%) and an error model parameter ε. This parameter is the probability that a homozygote is misclassified as a heterozygote and the probability that a heterozygote is misclassified as a homozygote. It is assumed that homozygotes are not misclassified as other homozygotes (113). We consider 3 settings for the parameter ε: 1%, 3%, and 5%. Each bar represents 2 values: power in the presence of errors (black portion of each bar) and PL, which is the difference of the power without errors and the power in the presence of errors (represented graphically as the red portion of each bar). Genotype frequencies for cases and controls are computed assuming the following genetic model parameters: f₀ = 0.01, f₁ = f₂ = 0.02, p_d = p₁ = 0.1, D′ = 1.0. That is, we assume a dominant underlying disease inheritance for the disease where the SNP marker locus is the disease locus. For a power of 99% at the 1% type I error rate, a minimum of 606 cases and 606 controls are required, given that we have equal numbers of cases and controls. Similarly, for a power of 80%, a minimum of 307 cases and 307 controls are required.