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Thanks for the help, Darren. Unfortunately, changing the F threshold did not change anything. I see no reason why the origins of the images should be a problem, and they appear to give perfectly reasonable (anatomically correct) answers when treated as one entire group. I also avoided an explicit mask in all the analyses. Any other ideas? -David -----Original Message----- From: Darren R. Gitelman [mailto:[log in to unmask]] Sent: Saturday, September 30, 2000 3:04 PM To: Kareken, David A. Cc: [log in to unmask] Subject: Re: 2-sample t-test Dear David: I think the message means that there ended up being no voxels whose significance passed the Upper tail F probability threshold. (Assuming that all con**.img images are appropriately oriented with the proper origins, etc. Also make sure you haven't masked the images at the second stage of the analysis. I suggest going into preferences and changing your F threshold to 1 (= no threshold) and rerunning your stats. HTH, Darren >SPMers, > Can someone help with the following message? I have a two group PET >activation study. I used a Condition x Subject model to generate con.img's >for each subject to take to a second (RFX) level analysis. When I enter >these two groups into this model, however, the analysis proceeds until the >last image plane/plank, and produces the following error output. > > Warning: No inmask voxels - empty analysis! > > In C:\Program Files\spm99\spm_spm.m at line 1074 > In C:\Program Files\spm99\spm_spm_ui.m at line 1427 > Design parameters : ...intrinsic >autocorrelation ...V, & traces ...scaling DesMtx >...closing image files ...smoothnessWarning: Divide by zero. > > In C:\Program Files\spm99\spm_spm.m at line 1137 > In C:\Program Files\spm99\spm_spm_ui.m at line 1427 > Warning: Divide by zero. > > In C:\Program Files\spm99\spm_spm.m at line 1138 > In C:\Program Files\spm99\spm_spm_ui.m at line 1427 > ??? Index exceeds matrix dimensions. > > Error in ==> C:\Program Files\spm99\spm_spm.m > On line 1142 ==> FWHM = FWHM*((RESEL/prod(FWHM(1:N))).^(1/N)); > > Error in ==> C:\Program Files\spm99\spm_spm_ui.m > On line 1427 ==> spm_spm(VY,xX,xM,F_iX0,xC,xsDes) > > By the first line, it appears to suggest that there are no voxels to >analyze. I submitted each of the groups separately, as well as one entire >group, to a one sample t-test to test the con.img's against a null >hypothesis and it works fine, producing the expected results. Thus, there >doesn't appear to be a particular problem with the images themselves. > > Suggestions? > >Thanks all. > >________________________________ >David A. Kareken, Ph.D., ABPP >Assistant Professor & Director >Neuropsychology Section, Department of Neurology >RI 5999C >Indiana University School of Medicine >Indianapolis, IN 46202 >(317) 274-7327 (voice) >(317) 274-1337 (fax) ------------------------------------------------------------------------- Darren R. Gitelman, M.D. Cognitive Neurology and Alzheimer's Disease Center E-mail: [log in to unmask] WWW: http://www.brain.northwestern.edu Voice: (312) 908-9023 Fax: (312) 908-8789 Northwestern Univ., 320 E. Superior St., Searle 11-470, Chicago, IL 60611 ------------------------------------------------------------------------- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%