On Mon, 2009-05-11 at 12:36 -0700, Anyuan Guo wrote: > Dear all, > I have P value of a list of markers. Now I need the chi square value > with degrees of freedom 2. > I noticed there are several Chisquare functions (dchisq, pchisq, > qchisq, and rchisq), but it seems all are not for my purpose. > In microsoft excel, there is a function CHINV to do this, such as > CHINV(0.184, 2) is 3.386, that means the chi square value for P value > 0.184, degree 2 is 3.386. > Does the R package has some function to do this? > > Thanks > > Anyuan
It never hurts to read the documentation: ?qchisq for example. Here "q" stands for "quantile." You want the Chi-square value that has 0.184 area to the left. To compute this: > qchisq(1-0.184,2) [1] 3.385639 You have to subtract 0.184 from 1, because qchisq finds the value with the given area below it. To double check the result: > 1-pchisq(3.385639,2) [1] 0.184 Rick B. ______________________________________________ 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.
