[R] Variance of expected survival based on a Cox model with frailty

Dear R users, I am interested in the expected survival probabilities of an example person, calculated on the basis of a Cox model with shared frailty. The example person has covariate values equal to zero and a frailty term equal to its expected value. I calculate the expected survival

[R] Testing strata by covariate interactions in coxph

Dear list members, I am working with a Cox ph model for the duration of unemployment. The event of interest in my analysis is getting employed. I have various background variables explaining this event: age, sex, education etc. I have multiple unemployment spells per person. I use a model with