> Suppose you find an activation cluster that you believe
> may originate from a small midbrain nucleus, and you want to test
> whether it is significant at a p-value that is properly
> corrected for multiple comparisons.
>
> One way would be to contrive a small-volume correction, after
> dredging PubMed to find suitable previous papers to justify your ROI.
> Hey presto, the small-volume correction will show that your cluster
> is significant. This doesn't feel quite right.
> (By the way, I'm not suggesting that all small-volume corrections
> are bad in this way, I'm just saying that it is unsatisfying here).
>
> Because the cluster is small, other multiple-comparisons correction
> methods will probably not count it as significant:
Clusters may be too small, but how about their t-scores? A small-volume
correction (SVC) reduces the severity of multiple comparisons, thus your
FWE-corrected threshold becomes much lower compared to a whole brain
analysis. I guess one of the motivations for an SVC is to avoid
correcting for multiple comparisons in areas you are uninterested at
all, thus to increase sensitivity in the area you are interested.
-Satoru
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