It may be the case that the result are not significant. If you have an
apriori region then you can analyze only in that region rather than
doing a whole-brain analysis. That will make the result more significant.
On 10/9/16 4:08 PM, Karamfil Bahchevanov wrote:
Hello Freesurfer experts,
I'm really struggling with my study.
I have a 27 scans that I analyze in QDEC. Scans are from Siemens
machine, mprage protocol, TR1620, TE 4.3, FOV 240*256, acq. matrix
232*256, slice thickness 0,9mm.
After I enter model and have some initial significant clusters
(threshold 2 - 5) I run multiple comparisons, and none have survived
the procedures, no matter method or significance - FDR
(0.1-0.05-0.01) or Monte-Carlo(0.05-0.01-0.01). This repeats no matter
of the tested variables and the initial significancy and size of the
clusters.
I'm really confused of that and could not find an explanation, except
that my study is really non-significant. However, the significant
results I get are in the regions that I expect to be, that are
reported previously and they also explain my results. If they happen
to survive, but that never is the case (In fact one survived, but I
entered wrong variables and model was wrong).
What could be the reason? Outliers? Really non-significant results
(which I doubt as I said already)? Should I recheck the quality of the
processed scans? I also made my own average, hoping to improve things
somehow, but QDEC doesn't allow me to run multiple comparisons with it.
Anyway, is it mistake to discuss the results when they don't survive
simulation, as they fit with initial hipothesis and what I'm testing.
I have to point that there are only few significant clusters, that
could not be explained with what I'm testing and tested population, so
in fact the "noise" is very small.
Any help will be of great value,
Thanks
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