Dimitri Liakhovitski
2011-Feb-10 20:43 UTC
[R] Chi square test of proprotions in 2 groups of different sizes
Hello! Very sorry for a probably very simple question - I looked but did not find an answer in the archives. I have a table "counts" (below) that shows counts by Option within each of my 2 groups. However, my groups have different sizes (N1=255 and N2=68). Table "prop" shows the resulting proportions within each group. I would like to compare the proportions in 2 groups using Chi Square test. However, I am not sure how to do it because chisq.test(counts) does not take into account the fact that the sizes of the groups are different. Any hint is greatly appreciated. Thank you! Dimitri G1counts <- matrix(c(54,76,125), ncol = 1) G2counts <- matrix(c(14,19,35), ncol = 1) counts<-cbind(G1counts,G2counts) colnames(counts)<-c("Group1","Group2"); rownames(counts)<-c("Option1","Option2","Option3") N1=255 N2=68 Ns=c(N1,N2) prop1<-G1counts/N1 prop2<-G2counts/N2 prop<-cbind(prop1,prop2) colnames(prop)<-c("Group1","Group2"); rownames(prop)<-c("Option1","Option2","Option3") (Ns);(counts);(prop);sum(prop)
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