# How to choose a sample size for two group repeated measures anova design given power, alpha, and effect size?

How would I go about computing the sample size for repeated measures ANOVA design, given power, significance and the required effect size (2 groups, I know the mean difference that I want to be able to catch and approximate standard deviation)?

• When you say you know the standard deviation, is this of the variables, or of the difference? (If the former, if you know the correlation, you can calculate the latter.) – Jeremy Miles Feb 28 '14 at 21:00
• You say this is between two groups. In that case, is there a reason to use ANOVA rather than a paired t-test? – David Robinson Feb 28 '14 at 21:01
• Maybe it's a RM ANOVA with a between-subjects factor? It's as if there weren't enough uncertainty in statistics already... – Nick Stauner Feb 28 '14 at 22:36

There's a nice tutorial on this which uses the R language/environment: