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st: adjusting hazard ratios in st cox using offset


From   Will Schairer <wschairer@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: adjusting hazard ratios in st cox using offset
Date   Mon, 15 Oct 2012 21:31:40 -0700

Hi all,

I have a dataset of procedures multiple follow-up events with an outcome of
a complication. There are a few procedures, proc_A, proc_B, proc_C, proc_D,
proc_E, which are all 0 -no- or 1 -yes-.

I'm trying to create an stcox model where the hazard ratios are in
reference to one of the procedures. Normally it would be fine just to set
"proc" = 1,2,3,4, or 5, and use the i.proc. However, in this data there can
be multiple procedures occurring in each visit, so I can't set just one
variable like stcox i.proc

So, I have:
var           HR
age
gender
proc_A     0.7
proc_B     1.2
proc_C     3.4
proc_D     3.2
proc_E     2.5

and I'd like to have:
var         HR
age
gender
proc_A     1.0
proc_B     ?
proc_C     ?
proc_D     ?
proc_E     ?

so that the ?'s are relative to proc_A = 1.0.

ok so my question is, can I use -stcox- age gender B C D E, offset(A) as a
way to normalize the other procedures to A? I have not found a good
detailed resource on offset, but my understanding is that it is an exposure
adjustment, so in a sense I'd be adjusting for exposure to proc A with HR =
1.0. Or, is there another way to do this?

Thank you!!

Will
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