I followed the TBSS v1.2 manual, and after creating .mat & .con files for a
two-sample unpaired t test, I ran the following randomise script for TFCE:
randomise -i all_FA_skeletonised -o tbss -m mean_FA_skeleton_mask -d
design.mat -t design.con -n 500 --T2 -V
Outputs generated:
tbss_tstat1
tbss_tstat2
tbss_tfce_p_tstat1
tbss_tfce_p_tstat2
tbss_tfce_corrp_tstat1
tbss_tfce_corrp_tstat2
Questions:
(1) Is tbss_tstat the raw, uncorrected t values? If it is raw and
uncorrected, should this t statistical map be identical to the tstat outputs
from using voxel-wise or cluster-based thresholding options?
(2) Is tbss_tfce_p_tstat the uncorrected p values? Am I right to say that
this is not corrected for FWE multiple comparisons, but TFCE is returning
uncorrected p-values that are specific to each cluster that is found? (I am
assuming this because some voxels have a higher uncorrected t-value but also
higher uncorrected p-value than other voxels located in other tracts. So
each found cluster follows its own t-distribution?)
(3) Is tbss_tcfe_corrp_tstat the FWE corrected p values? Thus, thesholding
this to .95-1 gives the clusters that survive a "p<.05 threshold, corrected
for multiple-comparisons?
I found several clusters that at 1-P=.95 level for tcfe_p_tstat, but no
clusters that survive at the 1-P=.95 level for tcfe_corrp_tstat. Is this
simply a power issue? This analysis has N=22 (11 in clinical group, 11
controls), but I am adding subjects to obtain N=34 (21 clinical, 13
controls) and will ultimately have N=100 (70, 30).
Thank you!
Mark Shen
UC Davis M.I.N.D. Institute
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