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_chuonggionho at yahoo.com>
To: "r-help at r-project.org" <r-help at 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]]
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