Dear SPMlers,
we have run an experiment with 15 Schizophrenics and 15 healthy
controls.
Our real voxel size is 3.59x3.59x3.6 (0.6mm gap).
Our data are normalized to a voxel size of 3x3x3 mm.
Now we want to compare the groups using different covariates in a 2nd
level analysis.
Here our question: What kind of spatial smooting is appropriate?
Standard is 2-3 times voxel size.
For group analysis the literature says to use 12-20mm.
As we have found effects when smoothing with 12 instead of 6 mm we are
considering using 15 or even 20 mm. (It is difficult to compare the
effects varying the smoothing systematicallly because every smoothing
needs 1.5 Gigabyte!).
Are there any principal arguments to stay with 12 or to use 15 or 20 mm?
If not which are the pragmatic arguments?
TIA
hw
--
Dr. Dr. Henrik Walter
Abteilung Psychiatrie III
Universitätsklinikum Ulm
Leimgrubenweg 12
89075 Ulm
fon: 0731/502 1489
fax: 0731/502 1549
e-mail: [log in to unmask]
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