Hi,
I am trying to analyze a couple of measurements of 4 subjects who are
measured under an active and a neutral condition repeatedly (4 times). After
carrying out the first level analysis seperately I started a higher level
analysis containing all 4 subjects. I set it up with 4 EVs (one for each
subject) and ran the analysis for the "active" and "neutral" condition
seperatly.
EV1 EV2 EV3 EV4
Subj1 1st Meas 1 0 0 0
Subj1 2nd Meas 1 0 0 0
Subj1 3rd Meas 1 0 0 0
Subj1 4th Meas 1 0 0 0
Subj2 1st Meas 0 1 0 0
.
.
.
Contrasts
Subj1 1 0 0 0
Subj2 0 1 0 0
Subj3 0 0 1 0
Subj4 0 0 0 1
After that I ran an analysis using the cope images from the analysis above
to get the group mean with one ev and all ones in the matrix
My first question: Is it now legal to use the resulting cope images of the
"active" and "neutral" conditions carried out similarly to get a contrast of
"active" more than "neutral", like to EVs one for each cope image and a
contrast with 1 -1 and -1 1 for both directions?
My second question: When I try to get that contrast in a higher level
analysis of only one measurement of one subject including only the "active"
and the "neutral" measurement (2 datapoints) with 2 EVs 1 0 (active) and 0 1
(neutral) with contrasts 1 0 (active only) 0 1 (neutral only) 1 -1 (active
more than neutral) and -1 1 (neutral more than active) flame complains about
the matrix being singular. Where did I make a mistake? I thought that this
analysis should be possible.
Thanks very much for any help with any of those questions.
Philipp Prahs
Dept. of Radiology - LMU Munich
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