Hello SPM experts!
I am having a problem which I think should have a simple solution, but I am just struggling to understand how to execute correctly.
I have an experiment where I have an experimental group and a control group. I succeeded in adding them as covariates at the second level, following the information provided in this previous post (https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=spm;43f44f54.0701). So basically now, in my second level I have my condition column, and my covariate column which indicates Control = 1 and Experimental = 0. However, I do not understand how to appropriately create a contrast that would allow me to make the comparison of Control Condition of Interest > Experimental Condition of Interest.
I tried an alternative way of adding the covariates as separate columns where Control = 1's wherever I have control subjects (0's elsewhere) and Experimental = 1 where I have experimental subjects (0's elsewhere). This to me, seemed more intuitive in terms of building my comparisons of interest, although I still doubt whether I am correctly creating my contrast. As an example, in this version where I have my 3 columns (condition, covariate 1 (Control) and covariate 2 (Experimental)), I thought that to compare Control Condition of Interest > Experimental Condition of Interest my T contrast vector should be [1 1 -1]. Would this be correct? If not, would someone be able to explain to me why and how to correctly make these comparisons? I am concerned that I am not fundamentally understanding how to assign comparisons when creating my contrast vector.
Thanks so much and I look forward to any help I can get,
Nadira
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