On Mon, 18 May 2009, Michel Boutsen wrote:
Hello
I would like to develop the use of R.
Trying R and more particulary the cox model, I am surprised by discrepancies
between results with stata and R for a cox model
With the same data base, I get a hazard ratio (4.82) that is not the same
obtained with stata (4.52)
I would expect that setting method = "breslow" replicates the results from
Stata (et al.). As ?coxph points out:
method: a character string specifying the method for tie handling.
If there are no tied death times all the methods are
equivalent. Nearly all Cox regression programs use the
Breslow method by default, but not this one. The Efron
approximation is used as the default here, as it is much more
accurate when dealing with tied death times, and is as
efficient computationally. The exact method computes the
exact partial likelihood, which is equivalent to a
conditional logistic model. If there are a large number of
ties the computational time will be excessive.
hth,
Z
You will find attached the file leukemia.dta I used (Stata)
Here are the codes for R
leukemia=read.fwf(file="leukem.txt",widths=c(4,2,3,2,5,2),col.names=c("id","TREAT","TIME","STATUS","LOGWBC",
"GENDER"))
library(survival)
res <- coxph(Surv(TIME, STATUS)~TREAT, data=leukemia)
summary(res)
and here the codes for for stata
infix ID 2-3 TREAT 6 TIME 8-9 STATUS 11 LOGWBC 12-16 GENDER 18 using
"g:rleukem.txt",clear
stset TIME, failure(STATUS==1)
stcox TREAT
SPSS and EPIinfo give the same HR than Stata
I tried with an other database without any problem
What would be the problem??? I changed of pc and versions of R (2.81 & 2.9.0)
without any change. The means are the same for the two packages.
I saw a few posts with discrepancies but not with the same database
Thanks in advance
Michel Boutsen
Brussel's University
Department of Biostatistics
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