> Is MVM still the right thing to do, even if I am interested in the covariate (i.e. Root_Fluency and Phon_Fluency),
> while controlling for the categorical variable (Morph)?
It's the variable types and data structure (not whether you're interested a particular variable) that determine which program to use.
> when trying to run 3dMVM I still get an error
What error did you get?
> -wsVars Morph \
> -bsVars "Root_fluency+Phon_fluency" \
> -qVars "MIE,Root_fluency,Phon_fluency,WM,Age" \
You didn't specify whether the variables "MIE", "WM" and "Age" are between- or within-subject?
Gang