Dear SPMers,
I haven't heard from any list members and I am still unsure how to proceed.
Any input would be greatly appreciated.
Our SPM2 model consists of four conditions, one for control subjects and the
other three each represent a different neurodegenerative disorder. We have
a single covariate of interest, two nuisance covariates and a global
correction factor.
For each degenerative group we’d like to determine where our covariate of
interest correlates with gray matter tissue that is not already explained by
the atrophy due to disease. We would also like to see if there are regions
correlated with the covariate across groups, again not explained by atrophy
vs. controls. Is it correct to model our covariate of interest as an
interaction? Does centering matter? And how would we generate contrasts
to answer the two questions above?
Many thanks,
Rich Crawford
UCSF Memory and Aging Center
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