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> Dear SPMers, I just realized that I originally sent this message out with the wrong subject heading.......Here it is again...... > > 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] > > > > >