[R] survreg() with frailty

[Dimitris Rizopoulos]

Dear R-users,

I have noticed small discrepencies in the reported estimate of the 
variance of the frailty by the print method for survreg() and the 
'theta' component included in the object fit:

# Examples in R-2.6.2 for Windows

library(survival) # version 2.34-1 (2008-03-31)

# discrepancy
fit1 <- survreg(Surv(time, status) ~ rx + frailty(litter), rats)
fit1
fit1$history[[1]]$theta

# OK
fit2 <- survreg(Surv(time, status) ~ rx + frailty(litter, df = 13), 
rats)
fit2
fit2$history[[1]]$theta

# discrepancy
fit3 <- survreg(Surv(time, status)~ age + sex + frailty(id), kidney)
fit3
fit3$history[[1]]$theta

# OK
fit4 <- survreg(Surv(time, status)~ age + frailty(id), kidney)
fit4
fit4$history[[1]]$theta


Am I missing something? Thanks in advance for any pointers!

Best,
Dimitris

----
Dimitris Rizopoulos
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/(0)16/336899
Fax: +32/(0)16/337015
Web: http://med.kuleuven.be/biostat/
     http://www.student.kuleuven.be/~m0390867/dimitris.htm


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