Dear SPMers,
I have some problems understanding why i get always different beta
parameters of the same subject data (same coordinate) looked in four
different ways (SPM99b):
a)Single subject analysis (just one subject in my design matrix).
I display the corresponding beta_1.img file, go to an arbitrary
coordinate and look at the beta (image intensity?) value.
b)Single subject analysis. Results -> go to same coordinate as above ->
plot contrast of parameter estimates -> effects of interest.
The value I get in the graph (the same as beta(1,1) in the matlab
terminal) is different than the value I obtained in a).
c) Fixed effects group analysis. In this case the data of my subject is
together with that of other subjects. Other than that the analysis is the
same as with the single subject analysis. I display the beta_##.img of the
subject I am interested in, go to the same coordinate as above and get a
beta value different from a) and b). Actually the whole beta image looks
completely different, as if it was that corresponding to a different
subject. But I checked that I am picking the correct beta_##.img.
d) Fixed effects group analysis. Results -> go to the same coordinate as
above -> plot contrast of parameter estimates -> effects of interest. The
beta(##,1) value is different than a), b) and c).
I was expecting to obtain the same beta values in these four ways of
looking at the same subject data. Any ideas of why this should not be the
case?
Thanks a lot,
Jorge
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Jorge Jovicich, Dr. rer. nat.
Dept. of Neurology | Computation and Neural Systems
Harbor-UCLA Medical Center | California Institute of Technology
1124 W Carson St. B-4 | 1200 E California Blv., BI 139-74
Torrance, CA 90502, USA | Pasadena, CA 91125, USA
310-222-5656/7 | 626-395-2882
310-222-5658 (fax) | 626-796-8876 (fax)
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