# Estimation of the baseline hazard in a generalized linear mixed-effects model (Poisson)

I need an estimation of the baseline hazard in a semi-parametric survival random effect model. Initially, I tried to do it with splines and the frailypack package. But frailypack does not accept stratification on a covariate which is in interaction with the random effect (slope()).

library(frailtypack)
data(dataAdditive)
modAdd <- additivePenal(Surv(t1,t2,event)~cluster(group)+strata(var1)+
var2+slope(var1),correlation=FALSE,data=dataAdditive,
n.knots=8,kappa=c(10000,10000))


I then tried to do it with generalized linear mixed-effects models with the family Poisson. This gives me an estimation of the piecewise baseline hazards. For this, I use the glmer function in the lme4package.

The problem is I need the estimation of the baseline hazard to be stratified on one covariate (which is in interaction with the random effect).

I have no clue of how to do it.

With the coxme function (coxme package), it is really simple. We just need to add a strataterm in the formula.

library(coxme)
library(frailtypack) #for the data
coxme(Surv(timeS,statusS)~strata(trt)+ trialID + (1|trialID/trt),data=gastadj)


Would anyone have a suggestion for me?

Thanks a lot !