Hi everybody,
I'm trying to complete a VBM analysis of some data I have and have a
number of questions about the correct usage of randomise which I'd
appreciate if someone could answer for me.
I have 3 groups (ctrl, long, and short) of 9 subjects each. I'm
attempting to ascertain whether there are grey matter differences
between these three groups.
I've set up the design matrix by following the FEAT example fro F
tests with 3 groups of subjects. So I have one input for each
subject, the first 9 are assigned to group 1, second 9 to group 2 and
final 9 to group 3.
I've added 3 EVs to the matrix with EV1 being 1 only for control
subjects, EV2 is 1 only for long subjects and EV3 is 1 only for short
subjects. I'v created 3 contrasts: ctrl - short, ctrl - long and long
- short and asked for 3 F-tests: one for each contrast in the Glm
window.
Does it look as if I've set up the design of this experiment
correctly? I've been reading the 3x3 thread on the FSl list in recent
days and am now a little confused as to whether I've set up my
experiment correctly or not.
I have, however, run a version of this experiment in randomise over
the night (the only difference to above was that the long - short
contrast was omitted) using the following command:
randomise -D -i GM_mod_merg_s2.5 -o grey005_s2.5 -d design.mat -t
design.con -n 1000 -F 6.66095 -v 5.75
and got the following files:
grey005_s2.5_max_tstat1.nii.gz grey005_s2.5_tstat1.nii.gz
grey005_s2.5_vox_tstat1.nii.gz
grey005_s2.5_max_tstat2.nii.gz grey005_s2.5_tstat2.nii.gz
grey005_s2.5_vox_tstat2.nii.gz
No _maxc_ files were produced. Why is that? Is it down to the command
line I used or the way I set up the contrasts?
Should I have provided the -f and -g options to randomise for this
experiment?
Thanks in advance,
--
Dr Colm G. Connolly
School of Psychology and Institute of Neuroscience
The Lloyd Building
University of Dublin
Trinity College, Dublin 2, Éire
Fax: +353-1-671-3183
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