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st: RE: Relative survival - strel


From   Nick Cox <n.j.cox@durham.ac.uk>
To   "'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Relative survival - strel
Date   Thu, 6 Oct 2011 11:39:14 +0100

As -strel- is not found by -findit-, it is especially important to explain to those curious where it comes from. 

Nick 
n.j.cox@durham.ac.uk 

Sam Leary 

I am a bit of a novice at survival analysis, but am trying to 
calculate relative survival using strel.  My variables are

death_5y = 1 if died by 5 years after diagnosis, 0 if still alive at 5 years
age_diag = age at diagnosis (years)
age_death = age at death or 5 years, whichever came first (years)

I have downloaded a lifetable which has the following variables:
country calendar_year sex age rate
and I have only kept the data for the calendar year relating to the start 
date of my audit.  I have also sorted this file by age then sex.

So I have used the following commands to calculate the crude and relative 
survival at 5 years after diagnosis:

stset age_death, failure(death_5y) origin(age_diag)
strel 0 5 using "ltab_s1",mergeby(sex)

My question is, as there are 257 deaths out of a total of 468, why is the 
crude survival percentage 41.86 using strel, rather than (468-257)/468 = 
45.1?


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