Dear SPMers,
I have a problem with entering a specific contrast in SPM which I cannot
quite explain.
I have two groups of subjects, both on and off drug, and two conditions on
and off drug
respectively.
I am interested in the main effect of drug in each group irrespective of
condition,
with the aim to run a conjunction analysis to look at drug effects across
groups.
I therefore enter two contrasts
a) 1 1 -1 -1 0 0 0 0
b) 0 0 0 0 1 1 -1 -1
SPM, however, only accepts b) as a valid contrast and states that contrast
a) is invalid.
Any ideas why that might be?
any help much appreciated!
Ines
Ines Goerendt
PET Neuroscience
Cyclotron Unit
MRC CSC
ICSM
Hammersmith Hospital
Du Cane Road
London W12 0NN
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