RE: Permutation test with small number of possible permutations

From: "Nick Holford" n.holford@auckland.ac.nz Subject: RE: [NMusers] Permutation test with small number of possible permutations Date: Fri, November 26, 2004 5:05 pm Mouksassi, This a good question. I am afraid I cannot help you with an algorithm to generate all possible permutations but I believe that in principle this is the correct approach. It is the underlying method of Fisher's Exact Test i.e. to compute P from all possible permutations of the data. The empirical methods of sampling at random from randomly generated permuations are easy to implement and usually the only practical method for anything more than small samples. I don't think that Stu Beal's commentary contained any substantive criticism of the basic method of employing a randomization test procedure to define a null distribution and estimate the P value. Indeed he has been co-author of a paper which have used exactly this method e.g. Zhang L, Beal SL, Sheiner LB. Simultaneous vs. sequential analysis for population PK/PD data I: best-case performance. J Pharmacokinet Pharmacodyn 2003;30(6):387-404. Nick -- Nick Holford, Dept Pharmacology &anp Clinical Pharmacology University of Auckland, 85 Park Rd, Private Bag 92019, Auckland, New Zealand email:n.holford@auckland.ac.nz tel:+64(9)373-7599x86730 fax:373-7556 http://www.health.auckland.ac.nz/pharmacology/staff/nholford/