Something has gone badly wrong here. For some reason, the estimated
smoothness is a FWHM of zero. I suspect it is because you didn't do any
grey matter thresholding.
For SPM analyses, the t statistic is proportional to the contrast value
divided by the square root of the residual variance. Where there is no
signal in your data, the residual variance is zero, and anything can
happen because of divisions by zero. This is why I would normally
suggest that only those voxels with intensity over about 0.05 are
included in the analysis. Supply an absolute grey matter threshold of
0.05, and you will hopefully get a more meaningful result.
Best regards,
-John
-----Original Message-----
From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]]
On Behalf Of Sophie Josee Lafaille
Sent: Monday, December 11, 2006 4:40 PM
To: [log in to unmask]
Subject: [SPM] NaN & outside clusters? repost
good morning, I was hoping to please get some help with these
questions, or maybe a reason as to why my results are this way? I have
searched the archives and found many similar questions, but no
answers. is there an answer?
thank you very much in advance, sophie
Dear SPMer's
I'm doing a VBM study in SPM5. matlab 6.5, latest updates.
2 groups, 16 per group, so 2 sample t-test.
attached is an example of our results.
I have 2 questions
1) why are my P corrected values listed as NaN?
2) why am I getting a cluster so far outside the brain and how do I fix
this?
thanks so much for any ideas you have.
sophie
----- End forwarded message -----
--
Sophie Lafaille, B.Sc.(Hons.), M.Sc.
Research Officer II, Speech Fluency Laboratory 1059
Graduate Department of Speech-Language Pathology
500 University Avenue, Toronto, Ontario, Canada M5G 1V7
Ph. 1-(416)-946-8635 Fax 1-(416)-978-1596
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