search for: age_at_death_yr

Hi, I'm having a bit of trouble with using StepAIC with a coxph model. Can anybody tell me if there is anything wrong with what I am doing here (I've removed a few of the variables for the purpose of this email, I had about 20 before): start<- coxph(Surv(entryage2,age_at_death_yr,death)~finih5+prev+magegp+zpluralgp ,data=project_model1) fmAIC1 <- stepAIC(start,direction="backward",scope=list(lower = ~ 1,upper = ~ finih5+prev+magegp+zpluralgp,data=project_model1)) This is the error I'm getting after it goes through a few times: Error in stepAIC(start, d...