# Calculating Sample Sizes

## Frequently Asked Questions

Where can I review the statistical theory behind these sample size calculations?

The sample size recommendations made on this site are all based on research done by Dr. James L. Kepner. For more information about discrete group sequential methods, see, for example, Jennison, C. and Turnbull, B.W. (2000), Group Sequential Methods with Applications to Clinical Trials, Chapman & Hall / CRC.

Who may use the results of these programs?

Please feel free to make use of the sample size calculator in your practice or research.

Whom can I contact if the sample size calculator will not work?

Although on-line user support is not currently available for this application, comments, suggestions, and corrections may be forwarded to Dr. James L. Kepner, Ph.D.

## Glossary of Terms

 Term or Phrase Definition Alpha The user-specified upper bound on the probability of making a Type I error, i.e. P(reject H0 | H0 is true) ASN Average Sample Number. (e1+e2)/2 Beta The user-specified upper bound on the probability of making a Type II error, i.e. P(fail to reject H0 | H0 is false) e1 The expected total sample size, given H0 is true e2 The expected total sample size, given H1 is true H0 The null hypothesis, i.e. H0: p=p0 H1 The research hypothesis, i.e. H1: p>p0 n(i) The sample size necessary at the ith (i = 1,2,...) stage of study p0 The value of p under H0 Power P(conclude H1 | H1 is true) S(i) The number of successes after the ith (i = 1,2,...) stage of study is completed Size The actual probability of committing a Type I error with the given design

* Please note that an understanding of additional terms may be necessary in order to comprehend the statistical analysis done on this site.