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AW: st: Different Results for the same estimation


From   "Martin Weiss" <martin.weiss1@gmx.de>
To   <statalist@hsphsun2.harvard.edu>
Subject   AW: st: Different Results for the same estimation
Date   Tue, 15 Sep 2009 22:24:45 +0200

<> 


You can always -collapse- or make up a fake identifier as 


-bys County disease: gen personid=_n-
-la var personid "Fake Identifier"-


To appreciate the meaning of this command, check Nick`s
http://www.stata-journal.com/sjpdf.html?articlenum=pr0004



HTH
Martin


-----Ursprüngliche Nachricht-----
Von: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] Im Auftrag von Johannes
Schoder
Gesendet: Dienstag, 15. September 2009 22:16
An: statalist@hsphsun2.harvard.edu
Betreff: Re: st: Different Results for the same estimation

Hi Martin:
Thanks a lot for your help.
Yes you are right I have nesting levels, within counties there are 
diseases that afflict individuals.
Unfortunately I messed (or the data provider) something up when 
importing the data. I just realized that I have a lot of individuals 
with the same identifier variable (although they are not the same), so I 
can't really use the id number.
Is there any alternative of aggregating the individual level data to the 
county level?
Johannes


Martin Weiss schrieb:
> <>
>
>
> So there are three nesting levels? Within counties, there are diseases
> afflicting individuals? If that is the case, you should amend your command
> as
>
> - bysort County disease (individual): keep if _n==1-
>
> to make it stable for the -glm- analysis. "individual" should be replaced
by
> some identifier variable, like an id number. 
>
>
> Also look at -egen, tag()- as -drop-ping is not generally the best
approach
> to conducting a restricted analysis ("How are you going to get the dropped
> obs back when you need them quickly?").
>
> Also look at -xtmixed- and its brothers, as your analysis sounds like a
good
> case for them...
>
>
> HTH
> Martin
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Johannes
Schoder
> Sent: Dienstag, 15. September 2009 20:17
> To: statalist@hsphsun2.harvard.edu
> Subject: Re: st: Different Results for the same estimation
>
> I found the bug:
>
> Since I am using the following command before the estimation:
> bysort County disease: keep if _n==1
> Stata probably kicks out different obervations eacht time.
> Does someone knows how to avoid that? A similar question was posed a 
> couple of days ago:
> How to delete duplicate observations,  Martin recommended the following 
> command that I used (see above):
>
> bysort ID: keep if_n==1
>
>
>
> However my problem is not exactly the same:
> Since I would like to aggregate my individual level data to the county 
> level I would like to just keep one observation for each county [instead 
> of keeping one observation per county I would like to keep 98 
> observations per county (one observation per county and per cancer type; 
> there are 98 different cancer types)].
> Therefore the observations I would like to drop are not the same 
> individuals, they just live in the same county and suffer from the same 
> disease.
>
> Thanks for your help!!
> Johannes
>
>
>
>
>
>
> Johannes Schoder schrieb:
>   
>> Dear Statalist users:
>>
>> When I am estimating the same model several times afterwards (with the 
>> same computer):
>> xi: glm [dep. var.] [indep. var.]  i.county i.year, family (binomial 
>> weight) link(logit)
>>
>> I get different results for the exactly same specification.
>> Does anyone know whats going on here? Is it because of the different 
>> number of iterations (sometimes 8,9 or 10)?
>> Which results are right? What can I do to get the identical result for 
>> the same estimation?
>> Thanks a lot for any suggestion!
>> Johannes
>>
>> *
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>>     
>
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