Is this the smallest observed dose that has an effect? If so, then you don't need the glm to find it. Here is a simulated example:
set.seed(101) X = rep(1:10,each=10) lp = -5 + 0.5*X Y = rbinom(length(X),size=1,p=1/(1+exp(-lp))) # is this the NOEL? min(X[Y==1]) # picks out observations with adverse effects, chooses the smallest value glmfit = glm(Y~X,family=binomial) plot(1:10, predict(glmfit,newdata=data.frame(X=1:10),type="response"), type="l",ylim=c(0,1),xlab="X",ylab="Y") rug(jitter(X[Y==0]),side=1) rug(jitter(X[Y==1]),side=3) On Tue, Apr 3, 2012 at 3:19 PM, Danielle Duncan <dldunc...@alaska.edu>wrote: > Thanks, that is interesting, but what I'm really after is an easy "no > observed effect level", using a binomial logistic model ie glm. Have a > great day! > > On Mon, Apr 2, 2012 at 3:38 PM, vito.muggeo <vito.mug...@unipa.it> wrote: > > > dear Danielle, > > > > The NOEL is a threshold value or breakpoint in the range of dose. Have a > > look to the > > package segmented to estimate a GLM with unknown breakpoints. The code > > (untested) should > > be something like > > > > library(segmented) > > o<-glm(y~1, family=binomial) > > os<-segmented(o, ~dose, psi=starting_psi) > > > > Also the package segmented includes the dataset down that can be useful > as > > an example.. > > > > data(down) > > with(down, plot(age, cases/births)) > > > > There is a paper of mine on R news 2008 discussing the package.. > > > > hope this helps you, > > vito > > > > > > > > On Mon, 2 Apr 2012 14:45:06 -0800, Danielle Duncan wrote > > > Hello, I used the glm function in R to fit a dose-response relationship > > and > > > then have been using dose.p to calculate the LC50, however I would like > > to > > > calculate the NOEL (no observed effect level), ie the lowest dose above > > > which responses start occurring. Does anyone know how to do this? > > > > > > [[alternative HTML version deleted]] > > > > > > ______________________________________________ > > > R-help@r-project.org 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. > > > > > > -- > > Open WebMail Project (http://openwebmail.org) > > > > > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org 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. > -- Drew Tyre School of Natural Resources University of Nebraska-Lincoln 416 Hardin Hall, East Campus 3310 Holdrege Street Lincoln, NE 68583-0974 phone: +1 402 472 4054 fax: +1 402 472 2946 email: aty...@unl.edu http://snr.unl.edu/tyre http://aminpractice.blogspot.com http://www.flickr.com/photos/atiretoo [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org 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.
