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Re: st: Testing equality across two specifications of ivreg2


From   Austin Nichols <austinnichols@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Testing equality across two specifications of ivreg2
Date   Wed, 5 May 2010 12:43:25 -0400

Jessica Ellen Leight <jeleight@mit.edu> :
This shows two specifications with the same sample:
http://www.stata.com/statalist/archive/2010-04/msg00373.html

On Wed, May 5, 2010 at 12:34 PM, Jessica Ellen Leight <jeleight@mit.edu> wrote:
> Dear all,
>
> I am estimating two different instrumental variables specifications using ivreg2
> on the same sample.  I have observations on two individuals per household (call
> them x1 and x2), each instrumented with an individual-level shock, and I
> estimate first the household fixed effects specification using the difference
> across individuals.
>
> ivreg2 ydif (xdif=shockdif), cl(village year)
>
> Subsequently, I estimate an individual's outcome as a function of both x1 and
> x2, appropriately instrumented, without household fixed effects.
>
> ivreg2 y1 (x1 x2=shock1 shock2), cl(county year)
>
> I now wish to test whether the coefficient on x2 in the second specification is
> equal to the coefficient on xdif in the first specification, or (a second test)
> whether _b[xdif]=_b[x2]-_b[x1].  Suest does not work smoothly with ivreg2 as
> others have noted, and previously suggested solutions on this list all seem to
> apply to cases in which the same specification is being estimated on two
> different subsamples, rather than two slightly different specifications with
> the same sample.
>
> Any suggestions are appreciated.
> Best,
> JL

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