Re: st: Why does one command "lose" observations compared to anothercommand?

[Suzy <scott_788@wowway.com>]

Hi Mike and Richard,

I used the same weight variable (mecwt4) for both the svy and non-svy 
commands. Also Stata on my PC is up to date as of a few days ago.

However, I did just now use a different weight variable for the non-svy 
command that I know for certain is 100% present for these variables. I 
did get back the proper # of observations (N=11,400). The point 
estimates are exactly the same as before.

If the mecwt4 variable loses some observations (which is certainly 
possible), why didn't it also lose those observations for the svy 
command?  In other words, shouldn't the svy command output have been =  
Subpop. no. obs = 10,568   rather than the 11,441?

Thank you for helping troubleshoot the problem!


mean age [pweight = wtint4yr] if age>=18, over(race)

Mean estimation                     Number of obs    =   11441

           1: race = 1
           2: race = 2
           3: race = 3
           4: race = 4
           5: race = 5

--------------------------------------------------------------
       Over |       Mean   Std. Err.     [95% Conf. Interval]
-------------+------------------------------------------------
age          |
          1 |   46.85757   .2383408      46.39039    47.32476
          2 |   42.29386   .3367213      41.63383    42.95389
          3 |   36.83151   .2716038      36.29912     37.3639
          4 |   41.38075   .8945132      39.62735    43.13415
          5 |   41.87601   .7078475       40.4885    43.26351
--------------------------------------------------------------



Michael S. Hanson wrote:


> On Jan 22, 2006, at 11:56 AM, Suzy wrote [slightly edited]:
>
> > I have come across a problem that I can't figure out. I don't know 
> > why I am "losing" 873 observations with one stata command versus the 
> > other -  for mean age by race, if age>=18. Both age and race are 100% 
> > present in the total dataset - total (N=21004) and for age>=18 
> > (N=11,441).
> >
> > Any insight into this would be greatly appreciated.
> >
> >
> > svy, subpop(if age>=18): mean age, over(race)
> >
> > mean age [pweight = mecwt4] if age>=18, over(race)
>
>     Have you examined mecwt4 to confirm that it has all 11441 
> observations in your restricted sample?
>
>                                         -- Mike
>
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