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Re: st: Restricting sample size


From   Nick Cox <[email protected]>
To   "[email protected]" <[email protected]>
Subject   Re: st: Restricting sample size
Date   Fri, 29 Nov 2013 11:07:11 +0000

Moreover, reducing sample size randomly won't remove or even reduce
any bias even if it's there. It will just increase imprecision. So,
this is a bad idea all round.

Nick
[email protected]


On 29 November 2013 10:48, Maarten Buis <[email protected]> wrote:
> On Fri, Nov 29, 2013 at 10:50 AM, Amal Khanolkar wrote:
>> The Swedish group is very large relative to the two other categories. As this might bias results for potential differences in outcomes of interest between the three ethnic groups (non-Europeans being very much smaller then the Swedish group), I would also like to run the analysis by reducing the Swedish group from 394,050 to say just 50,000 or 100,000 subjects. How would I tell Stata to run the above analysis restricting to a random sample when ethncity_bi2x==1  (i.e. the Swedish group) ?
>
> Why would the Swedish case be biased? The large sample size means that
> your Swedish estimates are a lot better then the other estimates.
> Reducing the quality of one estimate such that all estimates are
> equally bad seems like a very unproductive strategy. Below is how you
> could do that, but please think again if this is really what you want
> to do.
>
> gen weight = .
> bsample 50000, weight(weight)
> eststo: regress syst bwtgestage_sd age byear i.conscript_office bmi
> height_cons ib2.education2 ib3.gestwk_catx2 [fweight=weight] if
> multibirth==1 & sex==1 & ethnicity_bi2x==1, cluster (mor_lopnr)
>
> -- Maarten
>
> ---------------------------------
> Maarten L. Buis
> WZB
> Reichpietschufer 50
> 10785 Berlin
> Germany
>
> http://www.maartenbuis.nl
> ---------------------------------
>
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