[R] Finney's fiducial confidence intervals of LD50

[Dieter Menne]

carlos riveira <carlos.riveira <at> yahoo.com> writes:

> 
> I am working with Probit regression (I cannot switch to logit) can anybody 
> help me in finding out how to  obtain with R Finney's fiducial confidence 
> intervals for the levels of the predictor (Dose) needed to
> produce a proportion of 50% of responses(LD50, ED50 etc.)? 

See the example in MASS on <dose.p>. Don't know if it is comes out the same as
SPSS, though.

ldose <- rep(0:5, 2)
numdead <- c(1, 4, 9, 13, 18, 20, 0, 2, 6, 10, 12, 16)
sex <- factor(rep(c("M", "F"), c(6, 6)))
SF <- cbind(numdead, numalive = 20 - numdead)
budworm.lg0 <- glm(SF ~ sex + ldose - 1, family = binomial)

dose.p(budworm.lg0, cf = c(1,3), p = 1:3/4)
dose.p(update(budworm.lg0, family = binomial(link=probit)),
       cf = c(1,3), p = 1:3/4)

Dieter