Re: [Rd] Error from wilcox.test
On Wed, 2 Jan 2008, Prof Brian Ripley wrote: Try exact = TRUE: the default switches to a normal approximation that will not be adequate in your extreme example. I've modified the code in R-devel to give an answer in such extreme cases, but note that the p-value is pretty inaccurate, and so is the coverage of the reported CI. On Tue, 1 Jan 2008, Wolfgang Huber wrote: When one of the two groups has only one member and the other one more than 49, wilcox.test will exit with the below error message, n=51; wilcox.test(1:n ~ 1:n==1, conf.int=TRUE) Error in uniroot(wdiff, c(mumin, mumax), tol = 1e-04, zq = qnorm(alpha/2, : f() values at end points not of opposite sign whereas with n=50 a result is returned: n=50; wilcox.test(1:n ~ 1:n==1, conf.int=TRUE) Wilcoxon rank sum test data: 1:n by 1:n == 1 W = 49, p-value = 0.04 alternative hypothesis: true location shift is not equal to 0 95 percent confidence interval: 1 49 sample estimates: difference in location 25 I wonder whether it would be worthwhile to make the wilcox.test function handle such (admittedly pathologic) cases more gracefully. Happy New Year to all - Wolfgang -- Wolfgang Huber EBI/EMBL Cambridge UK http://www.ebi.ac.uk/huber -- 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, UKFax: +44 1865 272595 __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
[Rd] Error from wilcox.test
When one of the two groups has only one member and the other one more than 49, wilcox.test will exit with the below error message, n=51; wilcox.test(1:n ~ 1:n==1, conf.int=TRUE) Error in uniroot(wdiff, c(mumin, mumax), tol = 1e-04, zq = qnorm(alpha/2, : f() values at end points not of opposite sign whereas with n=50 a result is returned: n=50; wilcox.test(1:n ~ 1:n==1, conf.int=TRUE) Wilcoxon rank sum test data: 1:n by 1:n == 1 W = 49, p-value = 0.04 alternative hypothesis: true location shift is not equal to 0 95 percent confidence interval: 1 49 sample estimates: difference in location 25 I wonder whether it would be worthwhile to make the wilcox.test function handle such (admittedly pathologic) cases more gracefully. Happy New Year to all - Wolfgang -- Wolfgang Huber EBI/EMBL Cambridge UK http://www.ebi.ac.uk/huber __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
Re: [Rd] Error from wilcox.test
Try exact = TRUE: the default switches to a normal approximation that will not be adequate in your extreme example. On Tue, 1 Jan 2008, Wolfgang Huber wrote: When one of the two groups has only one member and the other one more than 49, wilcox.test will exit with the below error message, n=51; wilcox.test(1:n ~ 1:n==1, conf.int=TRUE) Error in uniroot(wdiff, c(mumin, mumax), tol = 1e-04, zq = qnorm(alpha/2, : f() values at end points not of opposite sign whereas with n=50 a result is returned: n=50; wilcox.test(1:n ~ 1:n==1, conf.int=TRUE) Wilcoxon rank sum test data: 1:n by 1:n == 1 W = 49, p-value = 0.04 alternative hypothesis: true location shift is not equal to 0 95 percent confidence interval: 1 49 sample estimates: difference in location 25 I wonder whether it would be worthwhile to make the wilcox.test function handle such (admittedly pathologic) cases more gracefully. Happy New Year to all - Wolfgang -- Wolfgang Huber EBI/EMBL Cambridge UK http://www.ebi.ac.uk/huber __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel -- 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, UKFax: +44 1865 272595 __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
