Solved
Contributor
Posts: 57

# Sample size calculation for three groups

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?

Best,

Accepted Solutions
Solution
‎12-12-2013 09:03 AM
Posts: 2,655

## Re: Sample size calculation for three groups

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

All Replies
Solution
‎12-12-2013 09:03 AM
Posts: 2,655

## Re: Sample size calculation for three groups

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

Contributor
Posts: 57

## Re: Sample size calculation for three groups

Thanks a lot Steve!

Do you think the approach I describe is also correct?

Best,

Posts: 2,655

## Re: Sample size calculation for three groups

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

🔒 This topic is solved and locked.