help for xsampsi

Sample size for AB/BA cross-over trials with continuous measures

This program will compute the required sample size for a simple crossover trial, that is AB/BA, or two-period two-treatment cross-over. It will estimate the power for a given sample size, too.

You must specify: alpha required significance level beta 1-power delta the difference between treatment arms stddev the standard deviation of this difference

You can specify: n different sample sizes, for which power will be computed

Requirements You must install the package nct (nct) for this program to work.

Comments This program essentially duplicates step by step the method that is given in Stephen Senn, "Cross-over trials in clinical research", 1993, on page 217. It is almost the same as a one-sample t-test for the difference between treatment, except that this method uses the non-central t-distribution, which gives you more accurate answers.

The variables are assumed to be normally distributed.

See also: sampsi, studysi

Written by Jan Brogger (jan.brogger@med.uib.no)