Thanks for the response, I should have clarified that the NOEL is the
smallest dose above which there is a statistically significant effect.

On Tue, Apr 3, 2012 at 12:44 PM, Drew Tyre <atyre2@unl.edu> wrote:

> 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 <dlduncan2@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.muggeo@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: atyre2@unl.edu
> http://snr.unl.edu/tyre
> http://aminpractice.blogspot.com
> http://www.flickr.com/photos/atiretoo
>

	[[alternative HTML version deleted]]

