Re: [R] logit GLM without intercept

From: Gavin Simpson <gavin.simpson_at_ucl.ac.uk>
Date: Tue, 22 Apr 2008 17:16:32 +0100

On Tue, 2008-04-22 at 17:04 +0200, gorgasal_at_gmx.de wrote:
> Hi Robert,
>
> you can exclude the intercept by including "-1" in the formula:
>
> value <- as.numeric(runif(20)<.4)
> ppm <- rnorm(20)
> glm(value~ppm-1,family=binomial)

Note that 0+ppm is the same thing, try it:

glm(value ~ 0 + ppm, family=binomial)

Your approach and that of Robert's are two ways to skin that particular cat.

G

>
> HTH
> Stephan
>
>
> > Dear Statisticians,
> >
> > I would like to analyse my data with a GLM with binomial error distribution
> > and logit link function. The point is that I want a model fitted without
> > intercept, i.e. the fitted curve should start at y=0.5 for x=0.
> >
> > I tried it with the following code:
> >
> > glm(value~0+ppm, binomial)
> >
> > Does this code yield the correct model or is there another possibility? I?d
> > appreciate it very much if you could help me out with this. I attached some
> > example data.
> >
> > Thanks & all the best
> >
> > Robert
>
> --
>
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Received on Tue 22 Apr 2008 - 16:33:33 GMT

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