Dear experts,

I just would like some confirmation whether what I do is correct. After
spending 3 days on the archives/other web resources I am still not
entirely sure.

I would like to determine the common activations between 2 groups of
subjects on 1 contrast. I would like to do this as a random effect
analysis.

The way I see it, there are 2 ways I can go about this:

Do a fixed effect analysis for all subjects (all subjects in 1 design
matrix) and then do a conjunction analysis on the same contrast over all
subjects. This would not really be a RFX analysis, but might allow for
some generalization to the wider population (if I have interpreted Friston
et al., 1999 correctly). Of course I would have to make sure that I have
the patch by Tom Nichols installed to make sure I am really performing a
logical AND conjunction.

Do a fixed effect analysis with a separate design matrix for each subject,
create the contrast for each subject. Then do a RFX conjunction analysis
over the 2 groups for that 1 contrast. I am assuming that since I only
take 1 contrast for each subject to the second level and since my 2 groups
consist of different subjects the sphericity assumption should hold.

I think the second option is probably the best, but it also presents me
with a few questions:
- Would a 2-sample t-test be good enough for me, since I compare 2 groups
on 1 contrast (in the archives, most advice centers around ANOVA and
regressions)?
- If so, how do I set up a 2-sample t-test without constant term?

I would appreciate any advice people can give me, please let me know if I
am going horribly wrong somewhere,

Bianca.