G*Power is a statistical power analysis program. It is a major extension of, and improvement over, the previous version, covering many different statistical tests of the F, t, chi-square, and z test families as well as some exact tests. G*Power 3 provides improved effect size calculators and graphics options, it supports both a distribution-based and a design-based input mode, and it offers five different types of power analyses. Like its predecessors, G*Power 3 is free.