On Mon, 31 Oct 2005, Prof Brian Ripley wrote: > On Sun, 30 Oct 2005, P Ehlers wrote: > >> [EMAIL PROTECTED] wrote: >>> Full_Name: foo ba baz >>> Version: R2.2.0 >>> OS: Mac OS X (10.4) >>> Submission from: (NULL) (219.66.32.183) >>> >>> >>> chisq.test(matrix(c(9,10,9,11),2,2)) >>> >>> Chi-square value must be 0, and, P value must be 0 >>> R does over correction >>> >>> when | a d - b c | < n / 2 ，chi-sq must be 0 >> >> (Presumably, you mean P-value = 1.) >> If you don't want the correction, set correct=FALSE. (The >> results won't differ much.) >> >> A better example is >> >> chisq.test(matrix(c(9,10,9,10),2,2)) >> >> for which R probably should return X-squared = 0. > > R is using the correction that almost all the sources I looked at suggest. > You can't go around adjusting X^2 for just some values of the data: the claim > is that the adjusted statistic has a more accurate chisq distribution under > the null. > > I think at this remove it does not matter what Yates' suggested (although if > I were writing a textbook I would find out), especially as the R > documentation does not mention Yates.
I have now checked Yates (1934), Fisher's 'Statistical Methods for Research Workers' and the Encyclopedia of Statistical Sciences. The first two are vague (and could perhaps be read as not correcting O-E = 0), but the latter agrees with R in giving a formula which always subtracts 1/2. Also, it mentions that Pearson stated that the formula for the continuity correction long preceded Yates' publication, so it is perhaps reasonable not to mention Yates. -- 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 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
