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Luis A. Afonso
Posts:
4,715
From:
LIsbon (Portugal)
Registered:
2/16/05


Re: NoNull HST . . .
Posted:
Feb 20, 2013 3:31 AM


The amazing ratio
In spite not to be expected a priori, the ratio between the numbers of functionally necessary permutations we have to consider and that potentially different a sample can provide is astronomically low. An example Consider two sized 30 sample X and Y we want to study the set of all differences of mean values. Let be X´ the pseudosamples 30 by 30 pairs formed among all 60 items: One is dealing exactly with 60C30 = 1.1826E17 pairs (U, V), denoting by V the sample of remaining items, after choosing at random U  Fisher´s Permutation Test. If we opt by intrapermutations we get 30!*30! = 7.04E64. In this instance to process them would be completely unfeasible, I suppose. Reality is quite different: I used with the Spider´s 1 million pairs with excellent output quality. The ratio is a *shameful* (1 /0.7)E65.
Luis A. Afonso



