Hi, I have a question regarding contrasts in linear models. I have a factor variable age with 4 levels, in the output of the linear model I want a coefficient for each level of age. I have made sure that age is a factor but am unsure how to put age into the model to ensure the model knows it is a factor an dto display all levels. I have tried doing fit<-lm(y~C(age)+sex.....) (the dot bits are the rest of the function which I have cut out as its not important here) but it only displays age as though it has one level what am I doing wrong and how can I get R to recognise its a factor? Thanks Jane ------------------------------------------------------ BA flight sale now at http://www.lycos.co.uk. Boston, ?129 rtn. including tax, Wednesday, 1pm
Contrast problem
2 messages · Jane McFerren, Brian Ripley
On Wed, 27 Nov 2002, Jane McFerren wrote:
I have a question regarding contrasts in linear models. I have a factor variable age with 4 levels, in the output of the linear model I want a coefficient for each level of age.
You can't get that, only 3 contrasts can exist for a 4-level factor. By default you get second - first, third - first and fourth - first.
I have made sure that age is a factor but am unsure how to put age into the model to ensure the model knows it is a factor an dto display all levels. I have tried doing fit<-lm(y~C(age)+sex.....) (the dot bits are the rest of the function which I have cut out as its not important here) but it only displays age as though it has one level
Is age really a factor (try is.factor)?
what am I doing wrong and how can I get R to recognise its a factor?
as.factor(age) will ensure that.
Brian D. Ripley, ripley at stats.ox.ac.uk 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 272860 (secr) Oxford OX1 3TG, UK Fax: +44 1865 272595 -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._