Dear SPMers,
I am analysing SPECT images of Lyme Disease subjects and I seem to be
running into "illegal contrast" problem. My design is as follows:
Lyme Patient Control Group Design type:
--------------- ---------------
Rest Challenge Rest Challenge Multistudy, different conditions
---------------------------------
1 0 -1 0
-1 0 1 0
0 1 0 -1
0 -1 0 1
---------------------------------
The objective is to compare individual Lyme patients against a group of
controls with the presence and the absence of Diamox. The program runs to
completion, but the output is very strange. The matrix of contrasts on the
SPM{F} page looks like:
0.5 -0.5 -0.5 0.5
-0.5 0.5 0.5 -0.5
-0.5 0.5 0.5 -0.5
0.5 -0.5 -0.5 0.5
What is interesting, a similar analysis in SPM'95 works fine.
Are these contrasts illegal? If so, what could be done to implement such a
design?
Many thanks,
Vitaly Furman
Brain Imaging Lab
Columbia-Presbyterian Medical Center
New York, NY
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