Dear StataList,
How can I calculate the sample size requirements for proportions in 3 (three) groups, namely: Control, Treatment1, and Treatment 2, when the outcome proportions typically range between 2% and 20%? Indeed, is it necessary to compare 3 groups - is it sufficient to compare Treatment1 vs Control and Treatment2 vs Control, and Treatment1 vs Treatment2, when I wish to establish that at least one of the treatment groups differs statistically from the Control group, and that Treatment1 differs significantly from Treatment2. Ideally, I would like to detect statistically significant differences between Controls and each of the treatment groups and between Treatment1 and Treatment2.
I will appreciate your expert comments.
Dora Pearce