Hi there,

I posted earlier about a design question and received a helpful response - but wanted to confirm one portion of it (I posted on the original thread, but I think it's getting lost in the mix).

The response to testing an interaction of post-pre differences between two conditions was the following:

"2) then in Setup.Conditions define your four conditions (e.g. pre_treatmentA, pre_treatmentB, post_treatmentA, and post_treatmentA) and associate each with the corresponding functional scan (this association may be common across all subjects or it may be different for different subjects, for example if the order of the two treatments was randomized across subjects). 

3) last, when you get to second-level analyses, select  AllSubjects in the 'subject effects' list, then select your four conditions in the 'Conditions' list and enter a vector [-1 1 1 -1] in the 'Between-conditions contrast' field. That will evaluate the interaction between your two factors (i.e. (post_treatmentA - pre_treatmentA) - (post_treatmentB - pre_treatmentB) )"

So, just to be clear...

Post-Treatment A = -1

Pre-Treatment A = 1

Post-Treatment B = 1

Pre-Treatment B = -1

Is this correct? I'm confusing myself I think.

Thanks so much!