Minimum sample size requirement (cases and controls) for case-control design for different values of SNP marker allele frequency. This figure provides the minimum number of cases and controls assuming the following genetic model parameters: f₀ = 0.0061, f₁ = 0.0184, f₂ = 0.0551, p_d = 0.2, and LD measure D′ = 1 between disease allele and marker allele A. Note that the penetrances satisfy the equations: f₁ = 3 f₀, f₂ = 9 f₀. The marker allele frequency is denoted by p_A and the disease allele frequency is denoted by p_d. Using the genetic model parameters, it follows that the prevalence of the disease is 0.012 (assuming that the 2 alleles at the disease locus are in HWE).