The issue is not 30 observations but whether it is possible to perfectly separate the two possible outcomes. Consider the following:
tst.glm <- data.frame(x=1:3, y=c(0, 1, 0)) glm(y~x, family=binomial, data=tst.glm) tst2.glm <- data.frame(x=1:1000, y=rep(0:1, each=500)) glm(y~x, family=binomial, data=tst2.glm) The algorithm fits y~x to tst.glm without complaining for tst.glm, but issues warnings for tst2.glm. This is called the Hauck-Donner effect, and RSiteSearch("Hauck-Donner") just now produced 8 hits. For more information, look for "Hauck-Donnner" in the index of Venables, W. N. and Ripley, B. D. (2002) _Modern Applied Statistics with S._ New York: Springer. (If you don't already have this book, I recommend you give serious consideration to purchasing a copy. It is excellent on many issues relating to statistical analysis and R. Spencer Graves Kerry Bush wrote: > I have a very simple problem. When using glm to fit > binary logistic regression model, sometimes I receive > the following warning: > > Warning messages: > 1: fitted probabilities numerically 0 or 1 occurred > in: glm.fit(x = X, y = Y, weights = weights, start = > start, etastart = etastart, > 2: fitted probabilities numerically 0 or 1 occurred > in: glm.fit(x = X, y = Y, weights = weights, start = > start, etastart = etastart, > > What does this output tell me? Since I only have 30 > observations, i assume this is a small sample problem. > Is it possible to fit this model in R with only 30 > observations? Could any expert provide suggestions to > avoid the warning? > > ______________________________________________ > 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 -- Spencer Graves, PhD Senior Development Engineer PDF Solutions, Inc. 333 West San Carlos Street Suite 700 San Jose, CA 95110, USA [EMAIL PROTECTED] www.pdf.com <http://www.pdf.com> Tel: 408-938-4420 Fax: 408-280-7915 ______________________________________________ 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