Hi Trinh, Please check ?dose.p() from library MASS.
Since you wanted the rate, the code was a bit modified from the example. > datPr X Event Trial 1 1210.0 8 8 2 121.0 6 8 3 60.5 6 8 fm<-glm(Event/Trial~X,data=datPr,family=quasibinomial(link=probit)) XD50<-dose.p(fm,cf=1:2,p=0.5) Dose SE p = 0.5: -203.7126 105.3647 XD50_CI<-XD50+c(1,-1.96,1.96)*attr(XD50,"SE") names(XD50_CI)<-c("XD50","lower","upper") XD50_CI XD50 lower upper -98.347938 -410.227309 2.802128 I am not very confident about the results though. A.K. From: phale_chuong gionho <phale_chuonggio...@yahoo.com> To: "r-help@r-project.org" <r-help@r-project.org> Cc: Sent: Monday, June 4, 2012 10:52 AM Subject: [R] probit analysis Hello! > I have a very simple set of data and I would like to analyze > them with probit analysis. > The data are: X Event Trial > 1210 8 8 > 121 6 8 > 60.5 6 8 > I want to estimate the value of X that will give a 95% hit > rate (Event/Trial) and the corresponding 95% CI. > you can help me? Thanks!! > Trinh [[alternative HTML version deleted]] ______________________________________________ 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. ______________________________________________ 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.