Re: [R] wilcox.test p-value = 0

2009-09-18 Thread Keo Ormsby
Hello, Thanks for the correction, sorry Murat I was mistaken. Actually your answers solved me a problem I was having using multiple fisher.test() on nucleic acid sequences, where we come up with hundreds of thousands of p values, a lot of which are 0's. Since we have to correct for multiple te

Re: [R] wilcox.test p-value = 0

2009-09-18 Thread Keo Ormsby
Hello Thomas and Bryan, Thanks for the correction, sorry Murat I was mistaken. Actually your answers solved me a problem I was having using multiple fisher.test() on nucleic acid sequences, where we come up with hundreds of thousands of p values, a lot of which are 0's. Since we have to correct

Re: [R] wilcox.test p-value = 0

2009-09-16 Thread Marc Schwartz
Once one gets past the issue of the p value being extremely small, irrespective of the test being used, the OP has asked the question of how to report it. Most communities will have standards for how to report p values, covering things like how many significant digits and a minimum p value

Re: [R] wilcox.test p-value = 0

2009-09-16 Thread Bryan Keller
That's right, if the test is exact it is not possible to get a p-value of zero. wilcox.test does not provide an exact p-value in the presence of ties so if there are any ties in your data you are getting a normal approximation. Incidentally, if there are any ties in your data set I would stron

Re: [R] wilcox.test p-value = 0

2009-09-15 Thread Thomas Lumley
On Tue, 15 Sep 2009, Keo Ormsby wrote: Hi Murat, I am not an expert in either statistics nor R, but I can imagine that since the default is exact=TRUE, It numerically computes the probability, and it may indeed be 0. if you use wilcox.test(x, y, exact=FALSE) it will give you a normal aproxima

Re: [R] wilcox.test p-value = 0

2009-09-15 Thread Keo Ormsby
Hi Murat, I am not an expert in either statistics nor R, but I can imagine that since the default is exact=TRUE, It numerically computes the probability, and it may indeed be 0. if you use wilcox.test(x, y, exact=FALSE) it will give you a normal aproximation, which will most likely be differen

[R] wilcox.test p-value = 0

2009-09-15 Thread Murat Tasan
hi, folks, how have you gone about reporting a p-value from a test when the returned value from a test (in this case a rank-sum test) is numerically equal to 0 according to the machine? the next lowest value greater than zero that is distinct from zero on the machine is likely algorithm-dependent