hi Diane

3dMEMA takes, for each subject, a map of betas and their associated t-statistics. when you entered:

-set groupA subA1 A1pre+tlrc A1post+tlrc subA2 A2pre+tlrc A2post+tlrc

3dMEMA thinks that subject A1 has A1pre+tlrc as the betas for that subject and A1post as the t-statistics corresponding to those betas, and proceeds accordingly.

When you say you switched the order of the time points do you mean you entered

-set groupA subA1 A1POST+tlrc A1PRE+tlrc subA2 A2POST+tlrc A2PRE+tlrc?

In that case, yes the results would be different, but in both cases the results are meaningless since you are telling 3dMEMA that (in the first case) the betas from the post condition for subject A1 are the t-stats corresponding to the betas for the pre condition.

Note if you wanted to use 3dMEMA's functionality to look at the group x pre/post interaction you could estimate the GLT of pre - post (or post-pre) at the single subject level and then use something like

-set groupA subA1 BETAS_FOR_PRE_VS_POST+tlrc T_STATS_FOR_THOSE_BETAS+tlrc

and likewise for the other subjects.

hope this helps.

James