Sample size calculation for multiple arm design

[Donia BOUZID]

Hello everyone,
I hope you are all doing well.
I have a friend that is designing a study evaluating the proportion of two biomarkers in three different populations of patients.
Population A is the reference
Population B would have a proportion of the two biomarkers (50 % compared to A)
Population C would have a proportion of the two biomarkers (25% compared to A)
I cannot find the way to do this calculation after reading the whole manual of power and sample size of Stata 15.
Thanks in advance for your help.

Donia

[Joseph Coveney]

You could refer your friend to the advice given in this Statalist thread.

Your friend's study seems to be an observational study or survey and not an experimental study where participants can be randomly allocated among treatment groups in equal numbers. So, another wrinkle in your friend's study is the relative availability for recruitment of patients in each of the three populations.