Good afternoon,
We are working on a multiple subject aging study with PET. We
have setup the experiment to study longitudinal trends in the PET signal. A condition
indicator models each time point (regularly spaced in time) and each subject
has an independent mean. We include age at the baseline scan as a covariate. Our
design matrix is located here: https://jshare.johnshopkins.edu/xythoswfs/webui/_xy-2399293_1
My question is: How does covariate centering work? When I
examine linear contrasts on the conditions (significance of trends), I see no differences
between centering age and not centering age? Is centering done automatically?
Regards,
Bennett
-------------------------------------------
Bennett
Landman, [log in to unmask]
Ph.D.
Candidate, Biomedical Engineering
Johns
Hopkins University School of Medicine