On Tue, 2008-01-15 at 11:15 +0100, LA SPINA, MICHELANGELO wrote: > Hello mailing list! > > I would like to know, how I can introduce a covariate in a glm, I've > two factors and a covariate. > > Thank you very much! > > ____________________________________________________________________ > Michelangelo La Spina
Hi, I'm not clear on the distinction between a factor and a covariate (I my way of thinking, a covariate is a variable that might predict an outcome or response variable). If you want to use the "covariate" as the response variable in a GLM then something like the following may be appropriate ## dummy data fac1 <- sample(gl(4, 25)) fac2 <- sample(gl(2, 50)) covar <- rnorm(100) my.dat <- data.frame(fac1 = fac1, fac2 = fac2, covar = covar) mod1 <- glm(covar ~ fac1 + fac2, data = my.dat) mod1 summary(mod1) # or if you already have a response variable and you want to include the covariate on the RHS of the formula, then one simple adds it in the same manner as we added the factors to the RHS above ## new dummy response my.dat$resp <- rt(100, df = 3) ## new model mod2 <- glm(resp ~ fac1 + fac2 + covar, data = my.dat) mod2 summary(mod2) Does this answer your question? G -- %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% Dr. Gavin Simpson [t] +44 (0)20 7679 0522 ECRC, UCL Geography, [f] +44 (0)20 7679 0565 Pearson Building, [e] gavin.simpsonATNOSPAMucl.ac.uk Gower Street, London [w] http://www.ucl.ac.uk/~ucfagls/ UK. WC1E 6BT. [w] http://www.freshwaters.org.uk %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% ______________________________________________ [email protected] 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.
