How many permutations do you think there are? Direct enumeration is only efficient for single-digit sample sizes, and those are too small to be interesting in practice.
The issue is to count them reasonably efficiently: if there are no ties this can be done inductively on the sample size, but otherwise it is a lot more complicated. On Wed, 21 Apr 2004 [EMAIL PROTECTED] wrote: > I can't figure out why it is not possible to compute an exact p-value in > cor.test if there are ties between values in one of the arrays like below: > cor.test(c(1,2,2), c(5,6,7), method="k", alternative="two.sided"). > > Perhaps this is due to my lack of understanding of what is ment by p-value > in this case. To me it seems reasonable that the p-value above should be > the number of permutations, normalized by the total number of permutations, > of one of the arrays that together with the other (unpermuted) array produce > a higer (or equal) absolute tau than than that of the original permutation. > I would be most greatful if someone cold help me understand the p-value > better. -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
