Approximate power to detect association between an allelic score indexing a biological exposure and disease.

The model is parameterized in terms of the percentage of variance in the biological intermediate explained by the SNP (σG2), the strength of the causal relationship between the biological intermediate (β) and liability of disease, which together determine the amount of variance in disease liability explained by the SNP (σL2), and the prevalence of disease. Estimates of power are presented for 2000 cases and 3000 controls (α = 0.05), and for 50000 cases and controls (α = 1.1×10−7).