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Antwort: st: re: Sargan test
From
Johannes Geyer <[email protected]>
To
[email protected]
Subject
Antwort: st: re: Sargan test
Date
Fri, 18 Feb 2011 15:11:02 +0100
> <>
> Sargan test of overidentifying restrictions
> H0: overidentifying restrictions are valid
>
> chi2(114) = 120.7602
> Prob > chi2 = 0.3145
>
>
> Sargan test of overidentifying restrictions
> H0: overidentifying restrictions are valid
>
> chi2(117) = 116.0779
> Prob > chi2 = 0.5067
>
> so, what could this tell you, and could we rely on these results.
>
> It quite clearly indicates that you cannot reject the null, which is
> a good thing. The p-value would have to be less than 0.1 or 0.05 to
> reject, so you are a long way from having any indicated problems
> with the instruments. However, heed David Roodman's advice in
> xtabond2 from SSC: the Sargan test is not very powerful when there
> are many instruments. Not knowing how many observations you have, I
> don't know whether 100+ instruments is a lot or a little.
>
> Kit
>
You can find some more details on this test in the pdf manual shipped
with Stata 11. E.g. heteroskedasticity is also a problem. Note that you
have to check the Ar2 test as well.
Two good introductory texts that came to my mind are
http://ideas.repec.org/p/cgd/wpaper/103.html
and
http://www.cemmap.ac.uk/wps/cwp0209.pdf
which cover the "Sargan test" or its robust version, the "Hansen test"
johannes
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