3dLME centering covariates within each condition

AFNI Message Board
1

Hi,

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:
-model “cond*RT+age”
-qVars “RT,age”
-qVarCenters “105.35,34.7”
-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?

Thank you!

Sincerely,
Christine

2

Christine,

3dLME currently does not have a mechanism to perform within-level centering for a within-subject factor. So you have to perform the centering for RT for each condition separately yourself, and then feed the numbers back into the table. After that, change the following line

-qVarCenters “105.35,34.7” \

to

-qVarCenters “0,34.7” \