st: Relative survival - strel

[Sam Leary <S.D.Leary@bristol.ac.uk>]

Dear all,  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?

Many thanks,

Sam.

----------------------
Dr Sam Leary
Senior Lecturer in Statistics

Working hours:
Monday, Tuesday and Thursday
7.30am - 2.30pm

Lifecourse Epidemiology and Population Oral Health Research Group
Department of Oral and Dental Sciences
Bristol Dental School
Lower Maudlin Street
Bristol
BS1 2LY
Tel 0117 342 3264
Fax 0117 342 4443
E-Mail: S.D.Leary@bristol.ac.uk
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