Getting all possible contingency tables
On 02-Dec-2012 14:17:20 Christofer Bogaso wrote:
Thanks Ted (and other) for your suggestion. Here I have implemented
following:
Tab <- matrix(c(8, 10, 12, 6), nr = 2)
Simu_Number <- 50000
Tab_Simulate <- vector("list", length = Simu_Number)
for (i in 1:Simu_Number) {
Tab_Simulate[[i]] <- matrix(rmultinom(1, sum(Tab), rep(0.25,
4)), nrow = 2) ## All Cells have equal probability
}
Sample_ChiSq <- sapply(Tab_Simulate, function(x) {
Statistic <-
sum((chisq.test(as.table(x))$observed -
chisq.test(as.table(x))$expected)^2/chisq.test(as.table(x))$expected)
return(Statistic)
})
length(Sample_ChiSq[Sample_ChiSq < qchisq(0.95, 1)])/Simu_Number
hist(Sample_ChiSq, freq = FALSE)
lines(dchisq(seq(min(Sample_ChiSq), max(Sample_ChiSq), by = 0.5), 1))
However I think I am making some serious mistake as histogram did not
match the density curve.
Can somebody help me where I am making mistake?
Thanks and regards,
[the remainder (copies of previous posts) snipped]
The reasons for the mis-match are: A: that you have put the curve in the wrong place, by not supplying x-coordinates to lines(), so that it plots its points at x = 1,2,3,4,... B: that you need to multiply the plotted density by the width of the histogram cells, so as to match the density curve to the discrete density of the histogram. It will also then look better when the chis-squared curve is plotted at the mid-points of the cells. Hence, try something like: hist(Sample_ChiSq, freq = FALSE, breaks=0.5*(0:40)) x0 <- 0.25+0.5*(0:20) lines(x0,dchisq(x0,1)) Hoping this helps, Ted. ------------------------------------------------- E-Mail: (Ted Harding) <Ted.Harding at wlandres.net> Date: 02-Dec-2012 Time: 15:02:45 This message was sent by XFMail