Dear R-help,
I am trying to estimate a Cox model with nested effects basing on the
minimization of the overall AIC; I have two frailties terms, both gamma
distributed. There is a error message (theta2 argument misses) and I
don?t understand why. I would like to know what I have wrong. Thank you
very much for your time.
fitM7 <- coxph(Surv(lifespan,censured) ~ south + frailty(id,
dist='gamma')+ frailty(mob, dist='gamma'), data= usa)
tempfun <- function(theta1, theta2) {
fit <- coxph(Surv(lifespan,censured) ~ south + frailty(id,
dist='gamma', sparse= TRUE, theta=theta1)+ frailty(mob, dist='gamma',
sparse =TRUE, theta=theta2), data=usa)
aic <- (fit$loglik[2] - fit$loglik[1]) - sum(fit$df)
return(2*aic)
}
nlminb(c(theta1=3.2,theta2=.2), tempfun)
Error in (get(temp))(x, ...) : argument "theta2" is missing, with no default
Best,
Silvia
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