Dear Otto,
|In the third column of the SPM report (voxel-level significances) there
|are several voxels with p>0.05. Why is that? Shouldn't in this column
|only be voxels which are significant at the 0.05 level after correcting
|for multiple comparisons based on the number of RESELs?
This depends on where you have set the global height threshold in the
results section. You can see what you have set it to at the very bottom
left of the output window (small text). Everything above this threshold
will be displayed.
|In addition, the fourth and fifth column (uncorrected k and Z) contain
|always the values 0.000. I understand that these are the uncorrected
|probabilities which need to be corrected by the # of RESELs. But how can I
|use these values if there are always 0.000?
This just means that they are too small to display in this format i.e.
p<0.001 would be how to report them. This would be the lowest conventional
global threshold that most people would be prepared to use, unless you
have some specific regional hypothesis in which case it would be best to
use the small volume correction tool to generate p values corrected for
this volume of interest.
best wishes,
Geraint
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Dr. Geraint Rees
Wellcome Advanced Fellow Lecturer
California Institute of Technology Institute of Neurology
Division of Biology 139-74 University College London
Pasadena 12 Queen Square
California 91125 London WC1N 3BG
voice (626) 395-2880 voice (171) 833-7472
fax (626) 796-8876 fax (171) 813-1420
http://www.klab.caltech.edu/~geraint [log in to unmask]
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