Hi DCR - Every year during sample size week in DCR, we get lots of questions about how to do sample size calculations when you want to look at change in a continuous variable from baseline to follow-up as your outcome. It's tricky to get the standard deviation of the change measurement, which is what is needed for the calculation.
This year, with help from our DCR faculty and statistician colleagues (notable Chuck McCulloch), we've developed a new 1-page handout to guide you through some of the considerations. You can find the handout under Materials in week three in the syllabus. This link also hopefully works.
If you think you might have this situation, take a look!
Mark