[R] Finney's fiducial confidence intervals of LD50

From: carlos riveira <carlos.riveira_at_yahoo.com>
Date: Mon 21 Aug 2006 - 22:03:50 EST


  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]]



R-help@stat.math.ethz.ch 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. Received on Mon Aug 21 22:08:17 2006

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.1.8, at Tue 22 Aug 2006 - 02:22:18 EST.

Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help. Please read the posting guide before posting to the list.