Introduction:

For chi-square tests use

pwr.chisq.test(w =, N = , df = , sig.level =, power = )

where w is the effect size, N is the total sample size, and df is the degrees of freedom. The effect size w is defined as

p0_i = cell probability in ith cell under H₀

p1_i = cell probability in ith cell under H₁

Cohen suggests that w values of 0.1, 0.3, and 0.5 represent small, medium, and large effect sizes respectively.