[R] offset in survreg
Ming-Wen An
man at jhsph.edu
Wed Oct 3 16:44:48 CEST 2007
Hello,
I have a question regarding the use of an offset term with survreg(),
in the Survival library. In particular, I am trying to figure out on
what scale the offset term should be.
Here's a simple example with no censoring and no coefficients:
---------
y = rlnorm(1000, meanlog = 10, sdlog = 2)
delta = rep(1, 1000)
int = rep(1, 1000)
survreg(Surv(y,delta)~offset(10*int), dist = "lognormal")
Call:
survreg(formula = Surv(y, delta) ~ offset(10 * int), dist = "lognormal")
Coefficients:
(Intercept)
-0.1317181
Scale= 1.985558
Loglik(model)= -11973.1 Loglik(intercept only)= -11973.1
n= 1000
---------
I would have expected the intercept estimate to be 10, since I
specified offset = 10, unless the offset term should be specified on
another scale.
Thank you,
Ming
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