Talk:Permutation test

Difference in results?

I see that the Tcl and Ursala code seem to be calculating different results. How can this be the case? I've been careful to check that the number of cases generated in the Tcl code is the correct one (92378 for selecting 10 from 19) so I think that's correct... –Donal Fellows 14:48, 1 February 2011 (UTC)

Shouldn't this be all combinations instead of all permutations? What difference does the order of members within the control or treatment group make (other than extra computation time)? --Rdm 16:08, 1 February 2011 (UTC)

I'm currently using "all combinations", which is reasonably fast (though I'm careful to treat each sample point independently, just in case there are repeated samples). All permutations is much slower (or it is if you generate directly) and I'm not sure how much difference it should make to the result since you'd effectively just be multiplying the number of each count by $m!n!$ (== 1316818944000 in this example; we'd be waiting a while for the result) and then dropping all that anyway when you average out. –Donal Fellows 21:46, 1 February 2011 (UTC)