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Hi, On 1 Mar 2008, at 02:07, Marenco, Stefano (NIH/NIMH) [E] wrote: > Our analysis outputs empty maxc_tstat1.nii.gz and > maxc_tstat2.nii.gz (max=0) > Is this the expected result for a negative finding (no significant > clusters) or did we do something wrong? If you check your raw _tstat images and see if there are any voxels above the cluster-forming threshold that you used in randomise, you should be able to see if there were any clusters that should have p- values in the maxc outputs. > Also, we are working on TBSS results. Regardless of the source of > the data, it is my understanding that variance smoothing is always a > good thing to do. Is this correct? Is there a rule of thumb on how > much variance smoothing should be applied (e.g. twice the voxel > resolution)? There's no clear rules on this I'm afraid. As Tom said recently, it is most useful for when you have a small number of subjects. You might alternatively consider using TFCE in randomise; we have not yet optimised the TFCE settings for TBSS-processed data, although you might try using --tfce_H=1 --tfce_E=1 --tfce_C=26 Cheers. > Stefano Marenco, MD > NIMH/GCAP > Building 10, room 4S235 > 10 Center Drive > Bethesda, MD 20892 > tel: 301 435-8964 > fax: 301 480-7795 > email: [log in to unmask] > --------------------------------------------------------------------------- Stephen M. Smith, Professor of Biomedical Engineering Associate Director, Oxford University FMRIB Centre FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK +44 (0) 1865 222726 (fax 222717) [log in to unmask] http://www.fmrib.ox.ac.uk/~steve ---------------------------------------------------------------------------