Hi Jason,
> Hello. I am using FSL scripts to extract information from
> statistical map images in certain ROIs. I am doing this by placing a
> threshold on the map and then finding information like: max z-score, mean
> z-score, number of voxels etc. However, by chosing a threshold this way
> (for example z=2.3) I am essentially using an uncorrected threshold. I
> know that if I want to do a Bonferroni correction in the ROI I can divide
> alpha by the number of voxels in the ROI.
Yup.
> But what if I want to do an FDR correction at alpha=0.5? Can I find
> the 95th percentile of all the z values in the ROI and use that as
> the threshold for the ROI? Would this then be considered FDR
> corrected at the ROI level?
No, it's not that simple. You have to compare the ordered P-values
p(i) to i/V (where V=number of voxels). There's a script FDR.m here
http://www.sph.umich.edu/~nichols/FDR
that will give you the threshold.
Hope this helps!
-Tom
-- Thomas Nichols -------------------- Department of Biostatistics
http://www.sph.umich.edu/~nichols University of Michigan
[log in to unmask] 1420 Washington Heights
-------------------------------------- Ann Arbor, MI 48109-2029
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