On Apr 22, 2011, at 1:37 PM, John Sorkin wrote: > > R 2.12 > windows 7 > > I am summary data that I would like to make into a 2x2 table representing > counts positive vs. negative counts: > 28/289 20/276 > > My table should look something like the following: > > group1 group2 > Positive 28 20 > Negative 289 276 > > How can a (1) create the 2x2 table > (2) run a chi square test on the table? > > I have tried the following code, but I don't know if it is correct, and it > does not give me an explicit 2x2 table: > >> xx <- c(28,20) >> pp <- c(317/(317+296), 296/(317+296)) >> chisq.test(xx,p=pp) > > Chi-squared test for given probabilities > > data: xx > X-squared = 0.8425, df = 1, p-value = 0.3587 >
Hi John, This is just a matrix. Thus, if you have the counts: x <- matrix(c(28, 20, 289, 276), byrow = TRUE, 2, 2) > x [,1] [,2] [1,] 28 20 [2,] 289 276 > chisq.test(x) Pearson's Chi-squared test with Yates' continuity correction data: x X-squared = 0.6491, df = 1, p-value = 0.4204 or as some might prefer: # No Yates correction, which is conservative > chisq.test(x, correct = FALSE) Pearson's Chi-squared test data: x X-squared = 0.9141, df = 1, p-value = 0.339 HTH, Marc Schwartz ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.