Department of Epidemiology & Biostatistics

Division of Biostatistics

Power and Sample Size Programs

This summary was originally prepared by Steve Shiboski in December, 1999. Last updated in October 2006.

You can view this summary organized by:

The same information is provided in each of the above links, it is just organized differently.

Type of Test


One or 2 sample comparison of means assuming a normal distribution are done by lots of programs and web sites.


Web Sites:


One or 2 sample comparison of means assuming a t-distribution are done by the following programs and web sites


Web Sites:


Several programs and web sites perform sample size and power calculations for 1-way and factorial ANOVAs. They differ with respect to how "effect size" is specified - with some it can be generated for you from treatment means that you specify, with others it is calculated as the ratio of between group to within group MSE, and others it is specified via the non-centrality parameter of the F distribution. Usually the null hypothesis is that the treatment means are all equal, but this isn't always the case. Usually treatment effects are assumed to be fixed, but a couple of programs have a "random" choice.



Simple Regression/Correlation

Effect size/alternative hypothesis is specified in various ways here, sometimes only by the r2 of the model.



More General Linear Models

A couple of people have contributed functions to StatLib for Splus and SAS.

Logistic Regression

From what I can gather only NQuery Advisor and PASS have this capability.


Several programs and websites will take care of this.



Chi-Square Contingency Tables

Some of these are restricted to the 2x2 or 2xM situation.



(Interestingly I didn't get these to agree.)

Survival Analysis

The input, and the flexibility they exhibit, is really varied. Most assume an exponential survival time.



Non Parametric Analyses

Only 1 software package dealt with this, PASS (for Wilcoxon & Mann-Whitney tests)

Operating System

The following programs are for use in MS-DOS or Windows environments:

The following work with a Unix operating system:

Don't forget all the web sites that are OS-independent:


The following programs are free:

The following programs cost $:

Admittably, these programs do a lot more than the others, without additional programming.


Click on the name of a program to find out more information about it.

Listing of Websites