On Tue, 22 Apr 2008, [EMAIL PROTECTED] 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)
Yes, but that is the same as 0 + ppm, which I tend to think is more intuitive. In so far as I understand the original question (what is 'y'?), either 0+ppm or ppm-1 will predict probability p = 0.5 at ppm = 0. > > 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 > > -- > > ______________________________________________ > 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. > -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ 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.