SAS and R produced different results for the same cox ph model on the same data

Question

I have fitted a Cox ph model using both R 4.3.1 and SAS 9.4 with the same data. In SAS, I used Proc phreg, while coxph function in Survival package, the model formula are totally the same, but I got different results (e.g., coefficients), what's the reason? And I wanan know how to modify my SAS program to get the same results as R, or modify my R code to get the same results as SAS.

Here is my data:

ID  Group    Time  Status WBC   CWBC    Gender
1   Treatment   6   1   2.31    Medium  0
2   Treatment   6   1   4.06    High    1
3   Treatment   6   1   3.28    High    0
4   Treatment   7   1   4.43    High    0
5   Treatment   10  1   2.96    Medium  0
6   Treatment   13  1   2.88    Medium  0
7   Treatment   16  1   3.6     High    1
8   Treatment   22  1   2.32    Medium  1
9   Treatment   23  1   2.57    Medium  1
10  Treatment   6   0   3.2     High    0
11  Treatment   9   0   2.8     Medium  0
12  Treatment   10  0   2.7     Medium  0
13  Treatment   11  0   2.6     Medium  0
14  Treatment   17  0   2.16    Low     0
15  Treatment   19  0   2.05    Low     0
16  Treatment   20  0   2.01    Low     1
17  Treatment   25  0   1.78    Low     1
18  Treatment   32  0   2.2     Low     1
19  Treatment   32  0   2.53    Medium  1
20  Treatment   34  0   1.47    Low     1
21  Treatment   35  0   1.45    Low     1
22  Placebo     1   1   2.8     Medium  1
23  Placebo     1   1   5       High    1
24  Placebo     2   1   4.91    High    1
25  Placebo     2   1   4.48    High    1
26  Placebo     3   1   4.01    High    1
27  Placebo     4   1   4.36    High    1
28  Placebo     4   1   2.42    Medium  1
29  Placebo     5   1   3.49    High    1
30  Placebo     5   1   3.97    High    0
31  Placebo     8   1   3.52    High    0
32  Placebo     8   1   3.05    High    0
33  Placebo     8   1   2.32    Medium  0
34  Placebo     8   1   3.26    High    1
35  Placebo     11  1   3.49    High    0
36  Placebo     11  1   2.12    Low     0
37  Placebo     12  1   1.5     Low     0
38  Placebo     12  1   3.06    High    0
39  Placebo     15  1   2.3     Medium  0
40  Placebo     17  1   2.95    Medium  0
41  Placebo     22  1   2.73    Medium  0
42  Placebo     23  1   1.97    Low     1

Time: Survival time

Status: 0 represents censorship

WBC: a continuous covariate

Here is my SAS program:

proc phreg data=mydata;
    class group(ref="Placebo");
    model time*status(0) = group wbc;
run;

And here is my R program:

library(survival)
library(survminer)
fit <- coxph(Surv(Time,Status)~Group+WBC,data=mydata)

Outputs:*

SAS gives

and R gives

Anyone can help? Thanks a lot!

Answer 1

The following bits from the documentation of each software will prove informative (highlights mine):

For PROC PHREG:

TIES specifies how to handle ties in the failure time. The following methods are available:
BRESLOW uses the approximate likelihood of Breslow (1974). This is the default value.

For coxph:

ties a character string specifying the method for tie handling. If there are no tied death times all the methods are equivalent. The Efron approximation is used as the default [..]

If you align these you'll see that you get identical results.