I have binary outcome (success & failure). Can someone advise me how can I compute sample size for 3 arm trial comparing 3 interventions. 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). So, can you 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 software which I could use.

I have tried g power, but I am unsure what should I use for following in g power:

Corr among rep measures = ?

Nonsphericity correction ε = ?

I will be thankful if you could advise me value which can be used for above 2 measures?

Other values which I could impute in g power are:

F tests - ANOVA: Repeated measures, within-between interaction

Analysis: A priori: Compute required sample size

Input: Effect size f = 0.5

α err prob = 0.05

Power (1-β err prob) = 0.80

Number of groups = 3

Repetitions = 4

Corr among rep measures =

Nonsphericity correction ε =

Thank you so much for your time.

Regards

Neha