Christine,
> My independent variable is Time. It has 4 levels and it is a repeated measure. I also have 3 nuisance
> behavioral measures that I would like to covary out of the analysis of the effect of Time. These three
> measures also change with the passage of Time (e.g., memory accuracy, memory confidence, and
> response time).
With within-subject covariates, 3dLME is definitely the solution for you.
> I would like to look at the effect of Time on brain activity with concomitant changes in those 3 nuisance
> measures covaried out.
Be careful about centering if each of those covariates has different means across the 4 levels of Time: [
afni.nimh.nih.gov]
> Would it also improve the model to include inter-subject differences in the three covariates? That is,
> should I include a component in the model that codes for differences in memory accuracy, memory
> confidence, and response time across participants?
I don't see any rationale for doing so if you've already incorporated those 3 covariates in the LME model.
Gang
