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Posted 07-16-2018 08:11 PM
(1165 views)

Hi SAS experts,

I'm conducting survival analysis where drugs that patients received are categorized to broad groups of biologic, chemo, hormonal, immuno and antibiotic (trt_other) in various combinations. My adjusted model produced Hazard Ratios for each treatment categories as shown in image below. However, I'm more interested in interactions of these five categorical treatments since treatments mostly had been prescribed in combinations. Contrast supposed to be used?

Any comments, hints or direct helps?

Thank you so much for your time!

```
data model;
input id duration vital_status1 trt_bio trt_chemo trt_hormone trt_immuno trt_other;
cards;
1 701 0 0 1 1 1 1
2 2123 1 1 1 0 0 0
3 2330 0 0 0 1 0 0
4 2513 1 0 1 0 0 0
5 57 0 0 1 0 0 0
6 1170 1 0 1 1 0 0
7 4032 1 1 1 0 1 0
8 2302 1 0 0 1 0 0
9 1230 0 0 1 0 1 0
10 1876 0 0 1 0 0 0
11 1503 0 0 1 1 0 0
12 2886 1 1 1 0 0 0
13 3941 1 0 0 1 0 0
14 584 0 0 1 0 0 0
15 1812 1 0 1 0 1 0
16 1025 0 0 1 1 0 1
17 3759 1 0 1 0 0 0
18 995 0 0 1 0 0 0
19 1297 1 1 1 0 0 0
20 770 0 0 1 0 0 1
21 263 0 0 1 1 0 1
22 472 1 0 1 0 1 0
23 490 1 0 1 1 0 0
24 1322 1 0 1 0 0 0
25 1940 0 0 1 0 0 0
26 103 0 0 1 0 0 0
27 887 0 0 1 1 0 0
28 2827 1 0 1 0 0 1
29 2251 1 1 0 0 0 1
30 3537 1 0 1 0 0 0
31 513 0 0 1 0 0 0
32 336 0 0 1 1 0 0
33 1402 0 0 1 0 0 0
34 2974 1 0 0 1 1 0
35 4248 1 1 1 0 0 1
36 3166 1 0 1 0 0 0
37 2053 1 0 1 0 0 0
38 2126 1 0 0 1 0 0
39 2236 0 0 1 0 0 0
40 898 1 0 1 0 0 0
41 645 0 0 1 0 0 0
42 113 0 1 0 1 0 0
;
proc phreg data=model;
class trt_bio(ref='1') trt_chemo(ref='1')
trt_hormone(ref='1') trt_immuno(ref='1')
trt_other(ref='1') /param=ref order=internal;
model duration*vital_status1(1)= trt_bio trt_chemo trt_hormone trt_immuno
trt_other/ties=Efron rl;
run;
```

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I don't think you need the CLASS statement at all here since you're working with binary variables. Don't you actually want zero as the reference for these? About the interactions, there are all sorts of handy shortcuts. For instance, if you have 4 variables (A, B, C, D) and you want all two-way interactions between them (plus the main effects, as usual), you can simply do this in the MODEL statement:

`MODEL time * event(0) = A | B | C | D @2 ;`

Where @2 indicates all two-way interactions, i.e.

A*B A*C A*D B*C B*D C*D

plus the main effects

A B C D

All described much better here (for GLM, but you can do the same in PHREG):

1 REPLY 1

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I don't think you need the CLASS statement at all here since you're working with binary variables. Don't you actually want zero as the reference for these? About the interactions, there are all sorts of handy shortcuts. For instance, if you have 4 variables (A, B, C, D) and you want all two-way interactions between them (plus the main effects, as usual), you can simply do this in the MODEL statement:

`MODEL time * event(0) = A | B | C | D @2 ;`

Where @2 indicates all two-way interactions, i.e.

A*B A*C A*D B*C B*D C*D

plus the main effects

A B C D

All described much better here (for GLM, but you can do the same in PHREG):

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