Power on X   (Mac OS X 10.3, 10.4, 10.5; cost $30 USD)
Power on X is an easy to use program for calculating the statistical power of tests. Calculations can be a priori (performed on data derived from a pilot or previous studies) or post hoc where the data has already been derived. At present Power on X will perform power calculations based on one and two-tailed t-Tests of means or correlations. The formula used to derive the algorithms used in the program are taken from:

Cohen J. Statistical Power Analysis for Behavioral Sciences. New York: Academic Press, 1969, 1977, 1988.

The calculator consists of a main calculation window in which the data can be entered and the type of test selected. In addition, an 'effect size' calculator is also included which can calculate 'effect size' from means and standard deviation, means and two standard deviations (requires sample size to be known), means and standard error of means (requires sample size to be known), and correlation.

In 'paid' mode the program will also produce power and sample size tables for any given alpha (significance) value.


  • Written in Cocoa and therefore Mac OS X native
  • Calculate power for one and two-tailed t-Tests
  • Calculate power for t-Test of means and t-Test of correlations
  • Perform post hoc and a priori power calculations
  • Calculate power tables for any given alpha (significance value) and a range of sample size

Why not give it a try?

The software is shareware ($30 US, approx. 17 GBP) and can be purchased through via:

Kagi - Buy Power on X

A demonstration version can be downloaded. The demo version has a disabled table feature and a 'nag' screen.

Further Information

Download Power on X