Dear SPM and FSL,
I've noticed that in SPM's function for converting uncorrected
p-values to FDR p-values (spm_P_FDR), there is a distinction drawn
between "corrected" and "adjusted" p-values, with reference made to:
Yekutieli & Benjamini (1999) (eqn 3)
http://dx.doi.org/10.1016/S0378-3758(99)00041-5
It is the *adjusted* p-values which spm_P_FDR actually returns, and so
I think these are the ones users report in their tables of voxel-wise
pFDR.
FSL's fdr program just saves a "q-rate" image, and experiment shows
that this matches SPM's "corrected" p-values (these aren't returned,
but are available, sorted, in Qs, which can be "unsorted" and turned
back into an image).
So my question is, are the "adjusted p-values" returned by SPM
preferable to the corrected ones / FSL's q-rate? Or should they be
differently interpreted? Incidentally, SPM's "Qs -> P" step can be
very slow for large images...
I have looked at the above reference, but I'm afraid I can't make
sense of the correction/adjustment distinction with relation to the
SPM code.
Many thanks to anyone who can help,
Ged.
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