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st: Problem with confidence intervals in stptime when using weights


From   "Dr. Till Ittermann" <Itterman@uni-greifswald.de>
To   statalist@hsphsun2.harvard.edu
Subject   st: Problem with confidence intervals in stptime when using weights
Date   Mon, 12 Mar 2012 12:26:58 +0100

Dear statalist,

I want to calculate age- and sex-specific incidence rates using pweights. In some of the age-and sex-specific subgroups incidence rates are very low. For these subgroups confidence intervals are not correctly calculated. This only happens when analysis are weighted. If no weights are used confidence intervals are correctly specified.

Example:

stset ftime [pweight = fweights], failure(diab_1=1) id(zz_nr)
bysort sex_0: stptime if diab_0 == 0, by(ag_kat) per(1000),

which will result in an output:

ag_kat | person-time failures rate [95% Conf. Interval]
-----------+---------------------------------------------------------------------------------------------
 20 - 29 years |    461611.79      528.7   1.1453347   .4140403    .4362638

I don't understand what is going wrong here. I tried several options of stptime incl. the jacknife option or enlarging calculations to 10000 person years, but nothing helped. Has anyone an idea how to solve this problem? I am using stata 12.1 with the latest updates.

Best,

Till





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