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Hi, On 16 Jan 2008, at 01:43, Yoshiko Yamada wrote: > Hi Steve, > > Thank you for your response! I have further clarification questions > regarding your reply to my third question. > > 1) Do I select the “cluster” option under “Thresholding”? I tried > both “voxel” and “cluster”, but I get the web report table only when > I selected “cluster”, so I hope this is right. (By the web report > table, I mean the table you see in “cluster_zstat1_std.html”. Is > this right?) That's right - at present you only get the web table if you select cluster-thresholding, and the corrected p-values are per cluster. > 2) By loading the thresh_zstat image onto FSLView, should I be able > to change the threshold by changing the number number in the Min > (and Max) window just above the images? It doesn’t let me change > threshold in FSLView, so I’m assuming that this is not possible. Yes, that's right - and you'll be changing the Z threshold by changing the Min intensity value. > 3) In the Cluster List in the“cluster_zstat1_std.html”, I see Z-MAX. > Are these z-values directly translatable into p-values? In other > words, if I see Z-MAX > 2.3, are the corresponding p-values < .01? Not exactly, Z values (including z-max) refer to voxelwise Z values, whereas in the cluster table, the p-values refer to whole clusters. Cheers, Steve. > > > Thank you in advance for taking time to reply! > > -Yoshiko > > > On Tue, 15 Jan 2008 06:23:54 -0000, Stephen Smith <[log in to unmask] > > wrote: >> Hi, >> >>> I have a few basic questions for clarification about FEAT post- >>> stats. >>> >>> 1) At each level of analysis, FEAT gives you tstat.nii.gz and >>> zstat.nii.gz >>> in the stat folder. Are >>> activations you see in these files not corrected for multiple >>> comparisons? >> >> These t and z-statistic images not p-value images are not even >> thresholded, so no they are not corrected for multiple comparisons! >> >>> 2) Do you have to choose either the voxel-wise or cluster-wise >>> thresholding in the FEAT post-stats >>> tab to have correction applied? >> >> Indeed - that's right. >> >>> 3) Does FEAT give you a zstat.nii.gz file which contain stats that >>> are >>> unthreholded but corrected for >>> multiple comparisons that we can load onto FSLView and look at >>> activations >>> at different thresholds? >> >> yes - you can set the p-value threshold to 1 so that no >> thresholding is >> done - then you can look at the "thresh_zstat" images in >> conjunction with >> the web report tables to see the (GRF-corrected) p-values. >> >> Cheers. >> >>> >>> Thank you very much in advance for your information! >>> >>> -Yoshiko >>> >>> >> > --------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------