Dear Dr Ruff,
The results should be identical. The parameter estimates
are not affected by the other subjects, and the con*.img images are
images of parameter estimates. A covariate for a given subject
will just include a column of zeros for every other subject, so this
covariate can contribute nothing to modelling any other subject's
data.
(The t and z statistics are different in these two cases,
however, since in the multi-subjects fixed-effects analysis the
within-subjects residual variance is estimated for all of the
subjects together. Provided all of the subjects have reasonably
similar variance, though, the results will be tend to be fairly
similar.)
Best wishes,
Richard Perry.
Dear SPMers
and staff,
I wonder
what is better for a random effect analysis :
1. To use
con*.img images from each single-subject analysis (little SPM.mat
easuy to load)
or
2. To use
con*.img images from single-subject contrasts of a global
multi-subjects analysis (big SPM.mat not so easy to
load...)
Thanks a
lot
Serge
RUFF
INSERM
U455
--
from: Dr Richard Perry,
Clinical Lecturer, Wellcome Department of Cognitive Neurology,
Institute of Neurology, Darwin Building, University College London,
Gower Street, London WC1E 6BT.
Tel: 0207 679 2187; e mail:
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