Thank you for your response. I had already checked and the faulty subject was not the "best target" chosen; it was a subject that had no artifact at all. In fact, after removing the faulty subject and rerunning 'tbss_3' the same subject with no artifact was chosen as "best target." So I still wonder why one faulty subject would apply its artifact to all others in the analysis? Is this a inherent problem while using the '-n' flag in tbss_2_reg?
After removing the faulty subject and rerunning tbss3-5, the resulting t-map and uncorrected p-map seem sensible and there are effects in regions that we predicted. However, none of these effects appear in the corrected p-map, even at extremely low (1-p=.3) threshold. Could this be explained by trying to remove a subject after tbss2?
Thanks for your help,
Mark
On Apr 16, 2010, at 9:22 AM, Gwenaëlle DOUAUD wrote:
Hi Mark,
> 1) Is it possible that 1 faulty subject with artifact could
> apply this artifact to all other subjects during tbss_2_reg
> and tbss_3_postreg?
Hmmm, the only way it could (well that I can think of) is if you were unlucky enough for your "best target" to be this "faulty" subject.
It must have been the case since the subjects didn't show the artifact after you've removed this subject and re-ran tbss3 (if you want to be sure, after running tbss3, the name of the best target is in best.msf, so this should change after removing the outlier)
> 2) Is it possible to remove a subject (and all associated
> files) from a TBSS analysis after tbss_2_reg has already
> ran?
I don't think this would be a problem.
> 3) Could the troubleshooting attempt in #2 affect the
> statistical analysis and power to detect direct
> between-group differences?
Unfortunately, I don't think so. Do your t-map/uncorrected p-map seem sensible?
Hope this helps,
Gwenaelle
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