[pymvpa] How you run permutation test for search-light analysis?
J.A. Etzel
jetzel at artsci.wustl.edu
Tue Mar 27 17:06:47 UTC 2012
I've played with versions of your procedure A before (threshold
individual subject maps, then calculate group-level frequency maps). It
strikes me as a justifiable method in some cases.
In the datasets I tried the group-level proportion maps were often
pretty similar to maps from t-tests. Something I found unsatisfactory
was the flexibility in deciding how to make and combine the binary maps:
calculate the proportion of subjects in which a searchlights' accuracy
is above 0.7 (i.e. a fixed threshold)? Or use a statistically-derived
threshold? Smooth the binary maps before combining? etc.
Your procedure B (bootstrapping the binary maps) is intriguing. One
thing I like about overlapping binary maps is that it dilutes the effect
of outliers (t-tests are very susceptible to outliers). Do you think the
bootstrapping could make outliers a problem again?
Jo
On 3/26/2012 7:41 PM, Francisco Pereira wrote:
> I tend to go for something like one of the two procedures below
> (Procedure A is analytical, Procedure B is nonparametric). I would
> love to hear comments, objections or to be told I'm completely wrong
> and should do otherwise :)
>
> cheers,
> Francisco
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