From: array chip <arrayprofile_at_yahoo.com>

Date: Mon, 18 Apr 2011 13:09:45 -0700 (PDT)

R-help_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Mon 18 Apr 2011 - 20:12:00 GMT

Date: Mon, 18 Apr 2011 13:09:45 -0700 (PDT)

Sorry this is a re-post. I posted it last night, haven't heard from anyone, hope
this moves the thread up a little and anyone can comment?

Thanks!

- Forwarded Message ---- From: array chip <arrayprofile_at_yahoo.com> To: r-help_at_r-project.org Sent: Sun, April 17, 2011 11:33:32 PM Subject: time dependent hazard ratios

Hi, I am new to time-dependent Cox model to estimate time dependent hazard ratios. Let me use aml dataset from survival package as an example:

> aml3<-survSplit(aml,cut=c(5,10,20),end="time",start="start",

This will generate the new data frame based on the time cut points 5, 10 and 20 and produce a indicator variable "i" that indicates the time interval membership for each observation.

If I want to esimate hazard ratio of variable "x" (Nonmaintained vs Maintained) for each of the time intervals 0-5, 5-10, 10-20 and >=20, would the following calculate such HRs?

> coxph(Surv(start,time,status)~x*as.factor(i),data=aml3)

Call:

coxph(formula = Surv(start, time, status) ~ x * as.factor(i),

data = aml3)

coef exp(coef) se(coef) z p xNonmaintained 19.2 2.10e+08 10461 0.00183 1 as.factor(i)1 NA NA 0 NA NA as.factor(i)2 NA NA 0 NA NA as.factor(i)3 NA NA 0 NA NA xNonmaintained:as.factor(i)1 -18.3 1.17e-08 10461 -0.00175 1xNonmaintained:as.factor(i)2 -19.6 3.18e-09 10461 -0.00187 1 xNonmaintained:as.factor(i)3 -18.0 1.46e-08 10461 -0.00172 1

So my understanding is that:

for time interval 0-5, HR=exp(19.2)=2.1e+08
for time interval 5-10, HR=exp(19.2-18.3)=2.46
for time interval 10-20, HR=exp(19.2-19.6)=0.67
for time interval >=20, HR=exp(19.2-18.0)=3.32

Am I correct on estimating these time dependent HRs?

Thanks

John

[[alternative HTML version deleted]]

R-help_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Mon 18 Apr 2011 - 20:12:00 GMT

Archive maintained by Robert King, hosted by
the discipline of
statistics at the
University of Newcastle,
Australia.

Archive generated by hypermail 2.2.0, at Mon 18 Apr 2011 - 21:10:30 GMT.

*
Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help.
Please read the posting
guide before posting to the list.
*