Build version: a57e8c3 (Feb 15, 2021)

PS is an interactive program for performing power and sample size calculations. It may be run as a web app at https://vbiostatps.app.vumc.org/ or downloaded for free. This version can be used for studies with dichotomous or continuous, response measures. An older version, which also handles other designs may be downloaded from http://biostat.app.vumc.org/wiki/Main/PowerSampleSize. Work on expanding the new version to handle all of the designs from the older version are in progress.

The alternative hypothesis of interest may be specified either in terms of differing means, or in terms of relative risks or odds ratios. Studies with dichotomous or continuous outcomes may involve either a matched or independent study design. The program can determine the sample size needed to detect a specified alternative hypothesis with the required power, the power with which a specific alternative hypothesis can be detected with a given sample size, or the specific alternative hypotheses that can be detected with a given power and sample size.

The PS program can produce graphs to explore the relationships between power, sample size and detectable alternative hypotheses. It is often helpful to hold one of these variables constant and plot the other two against each other. The program can generate graphs of sample size versus power for a specific alternative hypothesis, sample size versus detectable alternative hypotheses for a specified power, or power versus detectable alternative hypotheses for a specified sample size. Multiple curves can be plotted on a single graphic.