topic Re: Sample size calculation for three groups in Statistical Procedures

Sample size calculation for three groups

AnalytX — Thu, 12 Dec 2013 08:33:04 GMT

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,

Re: Sample size calculation for three groups

SteveDenham — Thu, 12 Dec 2013 14:03:44 GMT

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

Re: Sample size calculation for three groups

AnalytX — Wed, 18 Dec 2013 12:38:08 GMT

Thanks a lot Steve!

Do you think the approach I describe is also correct?

Best,

Re: Sample size calculation for three groups

SteveDenham — Wed, 18 Dec 2013 18:34:35 GMT

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