[pymvpa] Cross-participant MVPA and controlling for traits of no interest

J.A. Etzel jetzel at artsci.wustl.edu
Tue Jul 12 15:25:33 UTC 2011

To clarify a bit: what are your features for the classification? I take 
it they're not voxel values/imaging data but rather some sort of 
behavioral measures?

As a general strategy I'd work hard to make sure the feature you don't 
want driving the classification is not present in the training data, 
rather than trying to adjust for it afterwords.


On 7/11/2011 3:39 PM, John Clithero wrote:
> Hi PyMVPAers -
> I have a bit of a thought problem (but also hopefully an implementation
> one):
> I am performing cross-participant classification (do they belong to
> group A or group B?) and that classification works quite well (I've
> tried several different algorithms and the leave-one-out CVs are all
> significant). However, there is a trait X that we wish to control for
> (using the trait X - which is something we are not interested in and
> would prefer to have no effect on prediction - as a univariate
> predictor, it also performs significantly well for predicting group A or
> group B in a simple logistic regression), and I am hoping for some help
> in determining the best option.
> One option that I've thought of involves running SVM regression on the
> residuals from the logistic regression (so, instead of SVM on 0s and 1s,
> give it the continuous variable of the residuals and run SVM
> regression). This would (I think) effectively ask if a multivariate
> analysis can predict the variance that remains in individual binary
> classification after we have accounted for trait X. Does this sound
> reasonable, or can an option be thought of to adjust CV post-hoc that
> takes trait X into account?
> And, if that does sound reasonable, is there a straightforward way to
> implement this test in PyMVPA?
> Thanks for humoring me and my thought problem.
> Cheers,
> John
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