Dear SPMers,
If I threshold a T-map at p=.01 and k=14 contiguous voxels, then I get a
Table that reveals the following information.
Expected voxels per cluster, <k> = 5.798
Expected number of clusters, <c> = 5.32
Search volume: S = 3036994 mm^3 = 30852 voxels =
763.3 resels
Voxel size: [3.8, 3.8, 7.0] mm (1 resel = 35.60
voxels)
I'd like to determine the effective false positive rate for individual
voxels in this T map. I assume that it's going to be less than .01 because
of the 14 contiguous voxel spatial extent threshold. Is the formula below
correct?
Voxelwise False Positive Rate = (5.798 voxels per
cluster)*(5.32 expected clusters)/(763.3 resels*35.6 voxels per resel)
= (30.8454
expected voxels)/(2.7173e+004 total voxels)
=.0011
Finally, if I performed a conjunction analysis using two T maps
thresholded in exactly the same way as above, then would the false positive
rate be .0011^2?
Many Thanks,
> Daniel Weissman, PhD
> Center for Cognitive Neuroscience
> Duke University
> Durham, NC 27705
> phone: (919)-681-1029
> fax: (919)-681-0815
> e-mail: [log in to unmask]
>
>
