Hi Anson,
> May I know what's the different between FDR, FWE and none when SPM2 asks
> about 'p value adjustment to control'?
Wow, that's a big one :) Basically, this is the famous "correction for
multiple comparisons" issue. When you do multiple statistical tests, the
more you do, the more likely your are to get false positive results just
by chance. Therefore, you need to correct for this so-called Type 1
error, either using the family-wise error (FWE) or the false discovery
rate (FDR) approach. Uncorrected does not do anything here to correct
for these multiple tests and should thus only be used to explore
results. You will find hundreds of hits on the mailbase (1) if you
search for this.
> The 3 attachments are generated using FDR, FWE and none respectively. The
> results are quite different. The scan was a blank EPI scan that the
> subject was asked to relax and laying still with eye closed. So I didnt
> expect any activations seen in the glass brains.
Well, REST is only random episodic silent thinking, the brain is not
really swithced off :) Also, from your desing matrix, it does look like
you do have multiple conditions when you enter 1 as a contrast, so check
that you really only look at this condition.
> Which one (FDR, FWE or none) should I use?
None is not good enough, really. Whether FWE or FDR is a matter of
discussion: the former is more specific, the latter more sensitive. Both
are statistically legitimate. You may want to read some of Tom Nichols
papers on this issue, which even I (and that says a lot!) understood.
Hope this helps,
Marko
(1) www.jiscmail.ac.uk/cgi-bin/webadmin?S1=spm
--
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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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