Dear SPM users,
I'm trying to do a repeated measures ANOVA in SPM but I'm not sure if I'm making it right and how exactly to code the main effects and interactions for my model.
I have a 2x3 design with sessions 2 (within subjects) and components 3 (between subjects; this factor can also be considered as within but as I'm comparing spatial maps of independent components, they are independent so can be treated as a between factor). I use the flexible factorial design and code 3 factors: subjects (18) and session (2) and component (3). Each cell contains 6 files and conditions are coded as:
subject session component
1 1 1
1 1 2
1 1 3
1 2 1
1 2 2
1 2 3
until:
subject session component
18 1 1
18 1 2
18 1 3
18 2 1
18 2 2
18 2 3
So far so good, my design matrix has the following columns:
2 (session)
3 (component)
18 (subjects)
6 (interactions)
I want to calculate the contrasts for:
1) main effect of session
2) interaction session x component
3) planned comparison session x component 3 (I'm particularly interested in that one)
According to what I found they should be like this:
1) 1 -1 0 0 0 (comp.) zeros(1,18) (subjects) 0.5 0.5 0.5 -0.5 -0.5 -0.5 (interactions)
but even this one is not accepted.
What am I doing wrong and how to code contrast 2 and 3?
Thank you very much for your help
Nikola
|