Hi all,
I have a 2 group by 2 condition mixed effects analysis, and want to test for a group by condition interaction. The groups have unequal numbers of subjects. Although I don't personally have a problem with Gang's notion of testing for differences between each group's condition contrasts to get the interaction (i.e., Group1(Cond1-Cond2) - Group2(Cond1-Cond2)), some collaborators do not prefer this approach, and I anticipate that reviewers may balk at this approach.
So, I would like to know the best way to test for the interaction in this case, using an omnibus test. In this case, is 3dMVM the only way to go? I had heard that 3dMEMA can take into account the statistic associated with each input contrast map, thus possibly allowing for an omnibus test of the interaction as opposed to a test for differences. Is this true? I had thought that the idea of using the contrast t statistic is only useful if you have some research question about the variability of your conditions, not if you want test for an interaction in a mixed effects analysis.
I apologize if this topic treads on similar conversations re: 3dMEMA/3dMVM, but I am still not clear on how 3dMEMA uses the input contrast statistics to allow for an omnibus test of the interaction, if my perception about that indeed is correct.
Thank you!
-Thomas
