Hi Chris,
> Hi! I have what I hope is a simple question. I am analyzing a dataset using the standard mask in spm5. However, for some participants the masking threshold is set to (0.8), other times it is set to (-inf). Are the analyses for all participants comparable? Or will switching between defaults create problems?
One reason I did not reply was I did not know exactly what you meant :)
I assume you generated con-images and used different mask thresholds for
that?
I do not think this created a problem per se for the statistics in each
individual subject. The problem I see is that you may have data in some
subjects (those with the more lenient threshold) where you do not have
data in others (those with the stricter threshold). This may be an issue
when calculating smoothness estimates, as well as when comparing those
images, or combining them in one analysis. I would therefore make sure
that all subjects have data in all voxels you want to analyze (for
example, mask all con-imges with a strict mask when/before taking them
to the next level). This is my 2 cents, but I may be all wrong.
Cheers,
Marko
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Marko Wilke (Dr.med./M.D.)
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Universitäts-Kinderklinik University Children's Hospital
Abt. III (Neuropädiatrie) Dept. III (Pediatric neurology)
Hoppe-Seyler-Str. 1, D - 72076 Tübingen
Tel.: (+49) 07071 29-83416 Fax: (+49) 07071 29-5473
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