Hi everyone, I have a doubt about the way to calculate 95% CI for coefficients in the stratified Cox proportional hazard models and your help is welcomed .
Say that I have a variable of interest Imi and a stratifying variable UV in a interaction model (since the interaction between Imi and UV is of interest for me and the interaction model has a better fit than the no-interaction model: library(survival) model1 <- coxph(Surv(start,stop, Status.time) ~ Imi + Imi:UV + strata(UV) + cluster(ID), weights = NB_Event, data=Data.unfold) Whereas it is pretty straightforward to calculate the coefficients (and associated HR) for each combination of Imi and UV, I am not sure about how to calculate the associated CI (note that, of course, I got the CI for the estimate of "Imi:UV" from the output of model1). Is it correct to calculate separately a model for each UV level and use the CI for the Imi variable to get the CI for the two levels of UV (see below) ? # 2 models (one per UV level) data.Low <- subset(Data.unfold,UV=="low") model2.1 <- coxph(Surv(start,stop, Status.time) ~ Imi + cluster(ID), weights = NB_Event, data=data.Low) data.High <- subset(Data.unfold,UV=="high") model2.2 <- coxph(Surv(start,stop, Status.time) ~ Imi + cluster(ID), weights = NB_Event, data=data.High) Alternatively, is there a way to get the CI directly from the output of the stratified model ? Many thanks Andrea Bertolo Université du Québec à Trois-Rivières 3351, bd des Forges C.P.500, Trois-Rivières (Québec) Canada G9A 5H7 _______________________________________________ R-sig-ecology mailing list R-sig-ecology@r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-ecology
