One other option. I usually find that when I do the chisq.test with exact p-value calculation, I find the p-values are nearly identical to the results when I use the approximation and get the warnings (I'm usually dealing with just a few bins with less than 5, and many bins with more than 5).
So frequently, when I'm using chisq.test in a program, and expect to do it many times, I'll sometimes eliminate the warnings this way: old.warn <- options()$warn options(warn = -1) < do the chisq.test here > options(warn = old.warn) This will suppress the warning messages. Hope this helps. Matt Wiener -----Original Message----- From: Uwe Ligges [mailto:[EMAIL PROTECTED] Sent: Wednesday, March 26, 2003 4:24 PM To: aprilsun Cc: [EMAIL PROTECTED] Subject: Re: [R] a statistic question about chisq.test() aprilsun wrote: > > Hi, > In the chisq.test(), if the expected frequency for some categories is <5, there will be a warning message which says > Warning message: > Chi-squared approximation may be incorrect in: chisq.test(x, p = probs) It's a warning message, not an error. It point's you to the problem that a number < 5 is not "large", whereas in theory "large" numbers are assumed when running this test. > I am wondering whether there are some methods to get rid of this mistake... Seems the ?chisq.test() doesn't provide more > options to solve this problem. Or, the only choice is to preprocess the data to avoid this situation? It depends on the problem. Fisher's exact test (or it's extended version) might be an alternative, see ?fisher.test and an appropriate statistics textbook. Uwe Ligges > Thanks a lot! > > aprilsun ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help ------------------------------------------------------------------------------ ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help