[R] R coxph Method=df (Question on methods)

Dear R help, ## Example from http://stat.ethz.ch/R-manual/R-patched/library/survival/html/frailty.html # Random institutional effect coxph(Surv(time, status) ~ age + frailty(inst, df=4), lung) I am trying to understand what exactly happens when method=df is used ? The R documentation pages says

[R] Method=df for coxph in survival package

I've been following the example in the R help page: http://stat.ethz.ch/R-manual/R-devel/library/survival/html/frailty.html library(survival); coxph(Surv(time, status) ~ age + frailty(inst, df=4), lung) Here, in this particular example they fixed the degrees of freedom for the random institutio