I am having the exact same problem as you are, and I've been digging at this question for a month and I think I know the answer. I think it comes down to 2 factors. First: SAS doesn't offer the option of using an exact test for proc SEQDESIGN, whereas EAST does. So one possible difference may be attributed to the use of exact vs. a standard z-test. Second is what variance assumption you are using, as @StatDave says in his reply. This one you can control in SAS. One assumption uses the variance under the null hypothesis and the other assumption uses the variance under the alternative hypothesis. Changing that alters the necessary sample size pretty drastically I have noticed. So in the code you posted, you are using the variance based on the null hypothesis (ref=nullprop) and I betcha a nickel that in EAST you are using variance based on the alternative hypothesis (ref=prop) which will result in a larger sample size requirement. Neither is wrong, just a choice you have to make. Call me if you want to discuss - this has been driving me crazy for the past month and I ended up contacting Cytel's technical support over it, so they get the real credit. I think SAS's technical documents do say this, but in a very non-straightforward way. Hopefully they update SEQDESIGN to include an exact text and also include an example about changing the variance assumptions in their technical documents.
... View more
