Now this may be a massively stupid question however...

I am trying to sort out a sample size calculation for an RCT based on proportions.

Group 1 (control) is 0.68
Group 2 (experimental) is 0.80
Delta would be 0.05

When I use the power command I get wildly different (6x higher) sample size needed than if I were to use this online calculator:

http://powerandsamplesize.com/Calcul...or-Superiority

I think it is because I cannot work out where to put delta... or I’m doing it wrong (most likely). But I trust stata more than the online one...

Any help would be gratefully received.