[pymvpa] high prediction rate in a permutation test

[J.A. Etzel]

On 5/18/2011 5:54 PM, Yaroslav Halchenko wrote:

>> As a practical matter, I sometimes calculate t-test p-values in the
>> early stages of analysis because they're so fast, then calculate
>> permutation tests for the final p-values. In some datasets the
>> p-values from the two methods are close, in others they've been far
>> apart, sometimes with the t-test p-values much less significant.
>
> It is the evening, and we already celebrated the successful  launch of our
> neuroscience software survey (I bet all of you participated already, didn't
> you?) --- Jo, could you please elaborate a bit more on above "fast t-test
> ->  permutations ->  p-values"? I might be missing something obvious ;)

I don't mean using the t-test p-values to help calculate the permutation 
p-values at all, just that they can sometimes be a good shorthand for 
how-clustered-are-the-subjects'-accuracies in the early stages of 
analysis. The variance of the subjects' accuracies can also be useful 
for this, of course.

Jo