I am analyzing data for a project in which we are assessing outcome measures at 3 time points. I am interested in whether changes over time are moderated by sex and another between-subjects grouping variable, and whether sex and my other grouping variable interact to influence changes over time. Is this actually a 3-way interaction? (sex x grouping variable x time point)? If so, do you know of any online power calculators that could tell me the number of subjects I would need in my study to find this type of interaction?