# [R] Finney's fiducial confidence intervals of LD50

Renaud Lancelot renaud.lancelot at gmail.com
Mon Aug 21 16:35:49 CEST 2006

```Sorry there was a typo in my previous reply:

> D50 <- 10^c(logD50 + c(0, -1.96, 1.96) * attr(logD50, "SE"))
> names(D50) <- c("D50", "lower", "upper")
> D50
D50    lower    upper
140.8353 103.3171 191.9777

Best,

Renaud

2006/8/21, Renaud Lancelot <renaud.lancelot at gmail.com>:
> I don't know what Finney's fiducial confidence interval is but if your
> problem is to handle the output of dose.p (from MASS), you can do as
> follows:
>
> > library(MASS)
> > Response <- c(0, 7, 26, 27, 0, 5, 13, 29, 0, 4, 11, 25)
> > Tot <- rep(30.5, 12)
> > Dose <- rep(c(10, 40, 160, 640), 3)
> > fm <- glm(Response/Tot ~ log10(Dose), family = quasibinomial(link = probit))
> > logD50 <- dose.p(fm, cf = 1:2, p = 0.5)
> > D50 <- 10^c(logD50 + c(1, -1.96, 1.96) * attr(logD50, "SE"))
> > names(D50) <- c("D50", "lower", "upper")
> > D50
>      D50    lower    upper
> 164.9506 103.3171 191.9777
>
> Best,
>
> Renaud
>
> 2006/8/21, carlos riveira <carlos.riveira at yahoo.com>:
> >   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.)?
> >   If the Pearson chi-square goodness-of-fit test is significant (by default), a heterogeneity factor should be used to calculate the limits.
> >
> >   Response<-c(0,7,26,27,0,5,13,29,0,4,11,25)
> >   Tot<-rep(30.5,12)
> >   Dose<-rep(c(10,40,160,640),3)
> >   probit<-glm(formula = Response/Tot~ log10(Dose), family=quasibinomial
> >   D50<- round(10^(dose.p(probit,cf=1:2,p=0.5)))
> >
> >   #This is what SPSS calculates. I would like to reproduce these results with R:
> >   #SPSS RESULTS:
> >   #PRNT50= 140,83525
> >   #CI = 98,37857;205,34483
> >   #Regr.coeff= 1,91676 (S.E.=0,16765)
> >   #Intercept=-4,11856 (S.E.=0,36355)
> >   Thanks a lot for your help.
> >
> >   Carlos
> >
> >  __________________________________________________
> >
> >
> >
> >         [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help at stat.math.ethz.ch mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > and provide commented, minimal, self-contained, reproducible code.
> >
>
>
> --
> Renaud LANCELOT
> Département Elevage et Médecine Vétérinaire (EMVT) du CIRAD
> Directeur adjoint chargé des affaires scientifiques
>
> CIRAD, Animal Production and Veterinary Medicine Department
> Deputy director for scientific affairs
>
> Campus international de Baillarguet
> TA 30 / B (Bât. B, Bur. 214)
> 34398 Montpellier Cedex 5 - France
> Tél   +33 (0)4 67 59 37 17
> Secr. +33 (0)4 67 59 39 04
> Fax   +33 (0)4 67 59 37 95
>

--
Renaud LANCELOT
Département Elevage et Médecine Vétérinaire (EMVT) du CIRAD
Directeur adjoint chargé des affaires scientifiques

CIRAD, Animal Production and Veterinary Medicine Department
Deputy director for scientific affairs

Campus international de Baillarguet
TA 30 / B (Bât. B, Bur. 214)
34398 Montpellier Cedex 5 - France
Tél   +33 (0)4 67 59 37 17
Secr. +33 (0)4 67 59 39 04
Fax   +33 (0)4 67 59 37 95

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