Thanks for responding. We typically set a more stringent threshold of 20k for 3.75mm voxel size to buttress against false-positives when FDR or FWE don't hold.
I was wondering more specifically about the routine SPM5 results output where clusters are assigned in the table a "corrected" and "uncorrected" p-value regardless of the voxel-wise correction. These p-values are noted to the left of the voxel-wise columns.
I was under the assumption that if FDR or FWE were not reached at the voxel-level, you could at least report ONLY those clusters that reached a good cluster-wise significance threshold increasing confidence in your results. The "uncorrected" column is simple enough, but what's the "corrected" column for cluster significance reflecting? (Size of cluster relative to the sizes of the other clusters / total clusters)...or something like that??
Regards,
Jeff
---- Michael T Rubens <[log in to unmask]> wrote:
> the extent threshold is not factored into the correction, i.e., it
> would be the same whether the cluster is 1 or 100. it just changes the
> output for visualization, and some groups have a standard threshold of
> 5 or 15 voxels. If you want cluster extents to factor into correction,
> check out RFT (random field theory).
>
> -Michael
>
> On Thu, Sep 25, 2008 at 8:45 AM, Jeff Browndyke <[log in to unmask]> wrote:
> > Hopefully this question isn't too simplistic, but in the SPM output FWE and FDR are explicitly stated for voxel-corrected p-values, but what is the means of "corrected" for the SPM "non-isotropic adjusted cluster-level" p-values? And, is the "set-level" p-value corrected already, if so by what means?
> >
> > Thanks for any education in this regard...the p corrected at the cluster-level has been bothering me for a while, but now enough to seek a definitive answer.
> >
> > Regards to all,
> > Jeff Browndyke
> >
>
>
>
> --
> Research Associate
> Gazzaley Lab
> Department of Neurology
> University of California, San Francisco
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