G*Power 3

G*Power 3 is a major extension of, and improvement over, G*Power 2. It covers statistical power analyses for many different statistical tests of the F test, t test, χ2-test and z test families and some exact tests. G*Power 3 offers five different types of statistical power analysis: A priori (sample size N is computed as a function of power level 1-β, significance level α, and the to-be-detected population effect size), Compromise (both α and 1-β are computed as functions of effect size, N, and an error probability ratio q = β/α), Criterion (α and the associated decision criterion are computed as a function of 1-β, the effect size, and N), Post-hoc (1-β is computed as a function of α, the population effect size, and N), Sensitivity (population effect size is computed as a function of α, 1-β, and N), G*Power 3 provides improved effect size calculators and graphics options. It supports both a distribution-based and a design-based input mode. G*Power 3 is available for Mac OS X 10.4 and Windows XP/Vista. G*Power 3 is free.