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

From: i.m.s.white <i.m.s.white_at_ed.ac.uk>
Date: Tue 22 Aug 2006 - 19:49:08 EST

Finney's method for finding the confidence interval for a ratio of parameters is quite simple and is probably described in his book 'Probit analysis'. It is also known as Fieller's method so an RSiteSearch on 'Fieller' might show something useful.

On Mon, Aug 21, 2006 at 08:46:24AM -0700, carlos riveira wrote:
> thanks a lot Renaud.
> but i was interested in Finney's fiducial confidence intervals of LD50 so to obtain comparable results with SPSS.
>
> But your reply leads me to the next question: does anybody know what is the best method (asymptotic, bootstrap etc.) for calculating confidence intervals of LD50?
>
> i could "get rid" of Finney's fiducial confidence intervals but only if there was a better method..
>
> any idea?
>
>
>
> Renaud Lancelot <renaud.lancelot@gmail.com> wrote:
> Date: Mon, 21 Aug 2006 16:35:49 +0200
> From: "Renaud Lancelot" <renaud.lancelot@gmail.com>
> To: "carlos riveira" <carlos.riveira@yahoo.com>
> Subject: Re: [R] Finney's fiducial confidence intervals of LD50
> CC: r-help@stat.math.ethz.ch
>
> 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 :
> > 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 :
> > > 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
> > > (link=probit))
> > > 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]]
> > >
> > > ______________________________________________
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> > > and provide commented, minimal, self-contained, reproducible code.
> > >
> >
> >
> > --
> > Renaud LANCELOT
> > D?partement Elevage et M?decine V?t?rinaire (EMVT) du CIRAD
> > Directeur adjoint charg? des affaires scientifiques
> >
> > CIRAD, Animal Production and Veterinary Medicine Department
> > Deputy director for scientific affairs
> >
> > Campus international de Baillarguet
> > TA 30 / B (B?t. B, Bur. 214)
> > 34398 Montpellier Cedex 5 - France
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> >
>
>
> --
> Renaud LANCELOT
> D?partement Elevage et M?decine V?t?rinaire (EMVT) du CIRAD
> Directeur adjoint charg? des affaires scientifiques
>
> CIRAD, Animal Production and Veterinary Medicine Department
> Deputy director for scientific affairs
>
> Campus international de Baillarguet
> TA 30 / B (B?t. B, Bur. 214)
> 34398 Montpellier Cedex 5 - France
> T?l +33 (0)4 67 59 37 17
> Secr. +33 (0)4 67 59 39 04
> Fax +33 (0)4 67 59 37 95
>
>
>
> ---------------------------------
>
> [[alternative HTML version deleted]]
>

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Received on Tue Aug 22 19:55:02 2006

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