rm wrote > I’m trying to set up proportional hazard model that is stratified with > respect to covariate 1 and has an interaction between covariate 1 and > another variable, covariate 2. Both variables are categorical. In the > following, I try to illustrate the two problems that I’ve encountered, > using the lung dataset.
> > The first problem is the warning: > > To me, it seems that there are too many dummies generated. > > The second problem is the error: Adding the main effect of cov2 allows the model to run library(survival) lung$cov1 <- factor(lung$ph.ecog, 0:3, c("zero","one","two","three")) lung$cov2 <- factor(lung$sex, 1:2, c("male","female")) sCox <- coxph(Surv(time, status) ~ strata(cov1) + cov2 + cov1:cov2, data=lung) df <- data.frame( cov1=factor(0:3, 0:3, c("zero","one","two","three"))[1], cov2=factor(1:2, 1:2, c("male","female"))[1] ) df sfCox <- survfit(sCox, newdata=df) plot(sfCox[1], conf=FALSE) lines(sfCox[2], col=2) lines(sfCox[3], col=3) lines(sfCox[4], col=4) -- View this message in context: http://r.789695.n4.nabble.com/Problems-with-coxph-and-survfit-in-a-stratified-model-with-interactions-tp4646096p4646241.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.