Dear all
Sorry if this has been answered before - can't find the anwwer in the
archives anyway.
I am trying to analyse a drug study in which subjects were scanned
on two occasions, once on drug, once on placebo. Blind, randomised,
counterbalanced. It seems to me that in the analysis of this
there are really 3 levels of variance - the within session
variance (modelled at the first level) and the between subject
variance (modelled at the second level) but also the
within-subject- but-between-session variance, which intuitively falls
between the two in terms of contribution to overall variance.
I have tried incorporating the between session variance in the first
level analysis to just generate a single contrast image per subject
which then feeds into a 1-sample t-test at the second level. This
gives very nice results. I have also tried doing it at the second
level by making 2 contrast images per subject, one for drug and one
for placebo then feeding these into a paired t-tests. This gives very
different (not nice at all) results.
Which is the better way to model this data?
Thank you!
Rebecca
Dr Rebecca Elliott
Neuroscience and Psychiatry Unit
Room G907, Stopford Building
University of Manchester
Oxford Road
Manchester
M13 9PT
Phone: 0161 275 7433
Fax: 0161 275 7429
e-mail: [log in to unmask]
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