Dear SPMers,
I am trying to put a covariate into an SPM analysis. The covariate is
based on visual analogue scales, and I suspect that different subjects
have used different levels on the VAS to mean the same degree of the
variable I am trying to measure. I therefore wonder if I shouldn't be
using "specific fit" for this covariate. Is this a reasonable thing to
do?
Secondly when I put the covariate in as "specific fit" it then asks for
11 items in each contrast vector. (I assume because I have 11
subjects). I entered 2 contrasts, 1 1 1 1 1 1 1 1 1 1 1 and -1 -1 -1 -1
-1 -1 -1 -1 -1 -1 -1, again is this reasonable?
Thanks for any "idiots guide to ...." suggestions.
Mark Daglish
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