R libraries for sample size justification

Steve Simon


There are a lot of good commercial and free sources for sample size justification. Note that most people use the term power calculation, but there is more than one way to justify a sample size, so I try to avoid the term “power calculation” as being too restrictive. Anyway, I just noted an email on the MedStats list that suggests two R libraries.

The MBESS R package

estimates sample size by setting a goal on how precise you want the confidence intervals to be. It has a nice function that looks at the confidence interval for R-squared that would be hard to find in most other places.

The pwr R package:

uses a more traditional approach that follows the effect size notation noted in Cohen’s book on sample size.

Key papers, books and website