[R] Permutations with samr
isabelle.rivals at espci.fr
Wed Apr 25 10:50:17 CEST 2007
I have a question regarding the samr package.
For a 2 class unpaired problem, with sample 1 of size N1 and sample 2
of size N2, samr computes at most (N1+N2)! permutations of the two
samples (if the user-supplied parameter nperms allows it). However,
there are only (N1+N2)/(N1!*N2!) DISTINCT permutations of the two
samples, so it seems to me that only these distinct permutations should
be taken into consideration. Of course, working with the (N1+N2)!
permutations and working with the (N1+N2)/(N1!*N2!) distinct
permutations will lead to the same correct result, but for a number of
permutations smaller than (N1+N2)/(N1!*N2!), the result will generally
I would be very grateful if someone could provide me an explanation
for the samr choice of the permutations.
Thanks for your help,
Dr. Isabelle Rivals - Maître de Conférences
Équipe de Statistique Appliquée - ESPCI
10 rue Vauquelin - 75231 PARIS Cedex 05
Tél : (00 33 1) 40 79 45 45
Fax : (00 33 1) 40 79 44 20
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