Sample size calculation for three groups

[AnalytX]

Hello everybody,

I would like to perform a sample size calculation for a study  in parallel design, 3 arms.

I do not use the GLMPOWER procedure but use the following code:

proc power ;

     twosamplemeans

     alpha=0.017

     meandiff=mean difference

     stddev=estimated stddev

     power=.8

     npergroup=.

     ;

run ;

In fact, I adjust the alpha level using a Bonferonni correction (0.05/3=0.017).

Is this approach a good one? If not, do you have any suggestions?

Thanks a lot in advance for your answer.

Best,

[SteveDenham · Accepted solution]

Take a look at Example 71.1 One-Way ANOVA in the POWER Procedure, or look at PROC GLMPOWER Example 44.1.  The latter has an explicitly worked example for calculation of sample size.

Steve Denham

[AnalytX]

Thanks a lot Steve!

Do you think the approach I describe is also correct?

Best,

[SteveDenham]

The Bonferroni correction is almost always too conservative, and consequently will lead to an increased sample size needed to detect a fixed difference with given power.

Steve Denham