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Thank you, that makes perfect sense. On Aug 20, 2009, at 2:23 AM, Steve Smith wrote: > Hi, > > Raw _tstat_ images are indeed voxelwise - however I suspect that you > are looking at _tfce_tstat_ images, which look at spatial extent, so > will change if you change your mask. > Does this make sense? You could still find that your corrp > (corrected p-values) are improved through a more restricted mask fed > into randomise. > > Cheers. > > > > On 19 Aug 2009, at 19:58, Kirlic, Namik wrote: > >> Hi, >> >> We have recently figured out how to use a mask to restrict the area >> of the >> skeleton evaluated in a DTI tbss group contrast of FA maps using >> randomise. It was our hope that the lesser number of comparisons >> would >> mean that the correction being done in the corrected p maps >> accurately >> reflects us taking in less territory. It had been our understanding >> that >> in a voxel-wise contrast, t values should not be affected by changing >> which voxels were evaluated, only p values. However, when we used the >> masks, our resulting t values were reduced overall, which leads us to >> believe that voxels are not evaluated independent of one another. >> Is this >> the case, and if so, does this mean that we cannot use a bonferroni >> type >> of correction ourselves based on the voxels we wish to consider? >> >> Thank you! >> >> >> >> >> >> >> >> The information in this e-mail is intended only for the person to >> whom it is >> addressed. If you believe this e-mail was sent to you in error and >> the e-mail >> contains patient information, please contact the Partners >> Compliance HelpLine at >> http://www.partners.org/complianceline . If the e-mail was sent to >> you in error >> but does not contain patient information, please contact the sender >> and properly >> dispose of the e-mail. >> > > > --------------------------------------------------------------------------- > 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 > --------------------------------------------------------------------------- Namik Kirlic Phenotype Genotype Project Athinoula Martinos Center for Biomedical Imaging 149 13th St., Rm2303 Charlestown, MA 02129 Tel: 617-726-8631 Fax: 617-726-1351