I just wanted to say that I'm seconding this request. I'm pretty sure that the solution you proposed is the correct one, but I seriously need someone double checking it.
The setup of contrasts in the factorials design is extremely confusing and not really documented in SPM.
Thanks in advance to anyone who might be able to shed some light.
Luca
-----Messaggio originale-----
Da: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]] Per conto di Aleksi Sihvonen
Inviato: mercoledì 12 luglio 2017 09:30
A: [log in to unmask]
Oggetto: [SPM] VBM: Multi-group correlation comparison
Hi,
this is my first post here. I hope some VBM professionals can help me out.
I am running a 3-group VBM analysis on SPM8 and I want to compared the correlations between the GMV/WMV and a behavioural score.
I have selected:
1. Full factorial and defined a factor "group" with 3 levels 2. Loaded the GM (or WM in another batch) images in the respective cells and assigned levels 1, 2, or 3 accordingly.
3. Defined one covariate for the behavioural score in a single vector 4. Under interactions, I have chosen "with Factor 1". Centering is Overall mean.
As for the contrasts, for comparing Group 1 > Group 2: 0 0 0 1 -1 0 etc.
Have I carried out this correctly?
Additional question: If I want to use for example two nuisance covariates, could they be implemented in a normal fashion and then the contrasts would just be: for comparing Group 1 > Group 2: 0 0 0 1 -1 0 0 0 where the two last zeros are for covariates?
Thank you for your answers.
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