Request for advice: sample size for 3 arm trial with binary outcome

[Neha Dewan]

Hello

I have binary outcome (success & failure). Can someone advise me how can I compute sample size for 3 arm trial (Grp1: Intervention A, Grp2: Intervention B, Grp 3: Intervention A+B) comparing grp1 vs grp2, grp 1 vs grp 3, grp 2 vs 3. Success will be determined as complete relief of symptoms and percentage of patients will be computed. In previous literature, I can find studies comparing intervention A with B and found that 64% patients had complete relief with intervention A and 31 % had complete relief with intervention B but I could not find studies evaluating success rate with A+B. I also have one additional group (combined A+B) which is not used in the literature. I will be assessing outcome at baseline, 6wk, 3m, 6m and 1yr FU. So, can you please suggest me with the command which I can use to compute sample size for my 3 arm trial in stata 15 or is there any other free software which I could use.

Thank you so much for your time.
Regards
Neha

[Phil Bromiley]

You didn't get a quick answer. You'll increase your chance of a useful answer by following the FAQ on asking questions - provide Stata code in code delimiters, Stata output, and sample data using dataex.

Almost every Stata procedure tells you the sample size it used for the estimates. This automatically takes into account things like missing data. Run the analysis you want and see what it gives you. Normally, this would be something like the number of subjects/patients.

[Neha Dewan]

ok..Thank you for your reply and advise Phil. I am actually looking for command/steps which I can use to calculate sample size for this 3 arm trial. I haven't started the trial yet. As my outcome will be in terms of percentage of patients with complete relief. While I was looking on stata, I could see sample size estimation command for comparing 2 independent proportions but could not sort out how can I compute sample size if I have 3 groups instead of 2 groups. I will surely go through FAQ to see if I can find something similar.
Thanks again
Regards
Neha