[R] How to pass a nested random effect with frailty in coxph() - survival package?

[David Villegas Ríos]

Hi,
I have a very simple Cox regression model in which I need to include a
nested random effect: individual nested in treatment. I know how to pass a
single random effect - e.g. frailty(id)- but how can I specify the nested
random (id nested in treatment) effect using frailty?
The equivalent in lme4 would be (treatment|id)

Thanks!

David

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