On Wed, Jan 22, 2014 at 4:05 AM, Gabriel Go.Es. <[log in to unmask]> wrote:
Dear SPM experts,


Sorry for such basic questions. I'm new to the longitudinal design and analysis, and I have some doubts I would like to clear.

I have two groups of 12 subjects each and a follow-up MRI of two years for each subject.
Factor 1 (group) : 2 levels (Gp1 and Gp2)
Factor 2 (longitudinal) : 2 levels (year1 and year2)

A) As I undesrtood I have to set a full-factorial 2x2 anova (Group x Follow-up MRI as above), but I've seen in some faqs that I actually have to set up a third factor "subjects" which is the number of subjects in my study, but as I have never set a full factorial design, I'm not sure on how to set this third factor.

You need to use the flexible factorial design and add subject as a factor. It can't be done in the full factorial design.

 

B) How and which would be the constrasts for the desing in A? I mean, to test the effect of the groups and/or the differences in year1 and year2.

You can not test for the effect of group in a repeated-measures design using contrasts in the GLM. You can only test the difference in year1 and year2 or the interaction between group and year.
 

C) Is it possible to introduce nuisance variables i.e. age in year1 and age in year two?

Not in a repeated-measures framework using the GLM.
 

D) how do I correlate any of the tested effects with a variable of interest?

I would subtract year1 from year2, this will create a difference image and eliminate the repeated measurements. Then you can use a two-sample t-test with a covariate.



Many thanks in advanced,
Gabriel