Dear SPM experts,
I´d like to set up a second level analysis controlling for multiple confounding regressors and I´d need some help with a couple of things:
1) Does the order in which I enter the covariates influence the results? I know that it does for parametric modulators since SPM uses spm_orth to orthogonalize the modulators. And yet another thing: if I create a .mat file with R containing one column for each nuisance regressor, can this be pass as 2 cell arrays, one for "names" and another for "values" of each regressor as we do for multiple conditions in the first level (names, onsets, durations)?
2) One of the nuisance regressors is a categorical variable, handedness, coded as 1,2,3. Should I use these values and then "No centering" in this case?
Thank you very much in advance for considering my questions.
Best wishes,
Noelia
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