G*Power is a free general power analysis program.
G*Power performs high-precision statistical power analyses for the most common statistical tests in behavioral research, that is,
- t-tests (independent samples, correlations, and any other t-test),
- F-tests (ANOVAS, multiple correlation and regression, and any other F-test), and
- Chi2-tests (goodness of fit and contingency tables).
- power values for given sample sizes, effect sizes, and alpha levels (post hoc power analyses),
- sample sizes for given effect sizes, alpha levels, and power values (a priori power analyses), and
- alpha and beta values for given sample sizes, effect sizes, and beta/alpha ratios (compromise power analyses).
The program may be used to display graphically the relation between any two of the relevant variables and it offers the opportunity to compute the effect size measures from basic parameters defining the alternative hypothesis. You may give the program to friends and colleagues who might find it useful; however, if you want to include G*Power on a shareware or freeware CD-ROM, or if you want to distribute it together with commercial software, you must ask the authors for permission.