[pymvpa] Pairwise classification

[Jonas Kubilius]

>
> I guess you should generate the pairs yourself.
>

Maybe I should phrase it differently then: why isn't pairwise
classification the default? Is it somehow inferior? Has some bias? I've
never used multiclass classification so I am not sure about the differences
between the two approaches.



> But pay attention that estimating the accuracy using "all" possible pairs
> of the
> test set incurs in an optimisitc bias. The pairs are not independent since
> they sometimes share one element. Having a test set of non-independent
> examples leads to optimistic bias. In order not to have that bias you
> should
> use instead the subset of non-overlapping pairs.
>

Thanks! I'm well aware of non-indepence issues.

Jonas
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