Use extractAIC in frailty cox model (estimated with coxph function, gaussian random effect) i obtaided> extractAIC(fit.cox.f)[1] 11.84563 8649.11736 but I don't know why I can't use the classic formulation of the AIC where the degree of freedom are the number of the parameter (in my case 3). -- View this message in context: http://r.789695.n4.nabble.com/extractAIC-tp3718096p3718096.html Sent from the R help mailing list archive at Nabble.com.