FIGURE 3—

Effect of the reliability (measurement error; Rho) of a phenotype on the relationship between effect size of a genetic association and the sample size required to achieve 50% statistical power to detect the effect at the genome-wide significance threshold of 5 × 10⁻⁸.

Note. For example, if one expects a genotype to explain 0.4% of the variance in a trait (R² = 0.004), then a sample of about 10 000 participants is required to achieve 50% power when reliability is 0.80, but a sample of 20 000 participants is required if reliability is 0.40. That is, with a sample of 20 000 instead of 10 000, instruments that are only one quarter as reliable provide the same power to detect the effect.