survit function and cox model with frailty
Giacomo - Here's just a guess, since I have no experience with this. Try adding a sixth variable to the data frame "temp", a variable named "id" with value c(1,1,1,1,1). Maybe that will do it ? This is consistent with your intention in setting individual=TRUE, and it will give the frailty() term that's already in the model something to work with. - tom blackwell - u michigan medical school - ann arbor -
On Mon, 19 May 2003 gc4 at duke.edu wrote:
Hi:
I have a question about the use of the survfit function after the
estimation of a cox proportional hazard model with a frailty term. My goal
is to estimate expected survival probabilities while controlling for the
group-specific frailty term.
First, I estimate a model of the following form:
model1 <- coxph(Surv(t0, t, d) ~ x1 + x2 + frailty(id), na.action=na.exclude,
data=My.data)
Then, I prepare a data frame:
temp <- data.frame(t0=c(0,365,730,1095,1460),
t=c(365,730,1095,1460,3000),
d=c(0,0,0,0,0),
x1=c(0,0,0,0,0),
x2=c(1.5,1.5,1.5,1.5,1.5))
I think I would need to enter a statement with respect to the frailty
term, but I don't know how.
Indeed, when I use the survit function with temp data frame, I get an
error message:
fit2 <- survfit(model1, newdata=temp, individual=TRUE)
Error in model.frame(formula, rownames, variables, varnames, extras,
extranames, :
variable lengths differ
Thank you very much,
giacomo
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