I am attempting to apply 3dLME to a within-subjects design that has one factor (with 5 conditions) and one within-subjects covariate (RT) that varies across the five conditions. I would like to center the covariate within each condition, but am unsure of how to express this in the syntax.
Example 2 from the afni 3dLME documentation explains how to specify centering like this:
-ranEff ‘~1+RT’ \
How would I change this to include the average RT for each of the conditions, as opposed to just the grand mean?