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st: dstdize


From   "Colin M Fischbacher" <Colin.Fischbacher@ed.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: dstdize
Date   Thu, 14 Aug 2003 19:03:10 +0100

I'm using Stata 8. I think there is a problem with -dstdize-, or I'm
overlooking something. In short, if you use an external reference
population to directly standardise rates by age and sex (as in the
example on page 291, vol 1 of the manual), the resulting standardised
rates are half of what they should be.

The sum of the weights for the standard population distribution (the
column of output headed P) should total to 1, but when you adjust for
age and sex it totals only to 0.5 (or the proportion for the sex being
tabulated) Here is an example:

use http://www.stata-press.com/data/r8/hbp
gen pop=1
dstdize hbp pop age_group sex, by(race sex) using (test_stan) print

[first part of output . . ]

-----------Standard Population-----------
           Stratum       Pop.     Dist.
----------------------------------------
  15 - 19   Female      11000     0.106
  15 - 19     Male      10000     0.096
  20 - 24   Female      16000     0.154
  20 - 24     Male      15000     0.144
  25 - 29   Female      16000     0.154
  25 - 29     Male      15000     0.144
  30 - 34   Female      11000     0.106
  30 - 34     Male      10000     0.096
----------------------------------------
Total:             104000
(7 observations excluded due to missing values)

-------------------------------------------------------------------
-> race sex= 1 Female 
                                  -----Unadjusted-----  Std.
                                         Pop.  Stratum  Pop.  
           Stratum       Pop.     Cases  Dist. Rate[s] Dst[P]  s*P
-------------------------------------------------------------------
  15 - 19   Female         14         0  0.233 0.0000  0.106 0.0000
  20 - 24   Female         13         0  0.217 0.0000  0.154 0.0000
  25 - 29   Female         19         1  0.317 0.0526  0.154 0.0081
  30 - 34   Female         14         0  0.233 0.0000  0.106 0.0000
-------------------------------------------------------------------
Totals:                    60         1    Adjusted Cases:      0.5
                                               Crude Rate:   0.0167
                                            Adjusted Rate:   0.0081
                                95% Conf. Interval: [0.0000, 0.0235]

The proportion of females in the 25-29 age group in the reference
population is 0.30 (not 0.154) and the adjusted number of cases should
be 0.95 (not 0.5) and the adjusted rate 0.0158, not 0.0081. Is this a
bug or my mistake?

Dr Colin Fischbacher
Edinburgh 


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