What is the relationship between sample size and the power to detect differentiation or selection?

• A. Larger sample size reduces power.
• B. Larger sample size increases power.
• C. Sample size does not affect power.
• D. Power depends only on allele frequencies.

Answer: (B)

The main idea is statistical power—the ability to detect a real difference or a real signal of selection when it exists. When you sample more individuals, your estimates of allele frequencies become more precise because the sampling error shrinks. This means the true difference in frequencies between populations, or the true signal of selection, is less likely to be masked by random noise. As a result, the test is more likely to reject the null hypothesis when there really is differentiation or selection, increasing power. In short, larger samples give you clearer, more reliable estimates, making it easier to detect real differences or selective effects. Remember that power also depends on how big the true effect is and on allele frequencies; very small effects require even larger samples to achieve high power, and there are diminishing returns at very large sizes, but the overall relationship is positive.