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st: Strange result


From   "levinsar" <[email protected]>
To   "Statalist" <[email protected]>
Subject   st: Strange result
Date   Tue, 28 Jan 2003 07:45:50 -0700

I ran svymean on a binomial varialbe and got a standard error of zero in a
by() category. Rather than an infinite sample size, the category has just
two observations -- a "0" and a "1" for values. Naturally the two outcomes
test significantly different, p<0.0001, which is obviously incorrect. Is
this explainable? (Output below.)

. svymean  daymore2, by(cnty40 ) subpop(yellowdaymore2)
Survey mean estimation
pweight:  allpstratwt5                            Number of obs    =
3369
Strata:   newstrat                                Number of strata =
8
PSU:      abtid                                   Number of PSUs   =
2948
Subpop.:  yellowdaymore2==1                       Population size  =
641703.91
----------------------------------------------------------------------------
--
Mean   Subpop. |   Estimate    Std. Err.   [95% Conf. Interval]        Deff
---------------+------------------------------------------------------------
--
daymore2       |
     cnty40==0 |   .6443059    .0114672    .6218213    .6667905    1.769245
     cnty40==1 |   .5815394           0    .5815394    .5815394           .
----------------------------------------------------------------------------
--



Arnold H. Levinson, PhD
Associate Scientist
Center for Research Methodology and Biometrics
AMC Cancer Research Center
303.777.8801
fax 303.239.3394
[email protected]
Assistant Professor
Department of Preventive Medicine and Biometrics
University of Colorado School of Medicine
[email protected]

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