G*Power

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, * ?2-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-?, significance level ?, and the to-be-detected population effect size) * Compromise (both ? and 1-? are computed as functions of effect size, N, and an error probability ratio q = ?/?) * Criterion (? and the associated decision criterion are computed as a function of 1-?, the effect size, and N) * Post-hoc (1-? is computed as a function of ?, the population effect size, and N) * Sensitivity (population effect size is computed as a function of ?, 1-?, 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.