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RE: st: RE: Econometrics question


From   kokootchke <kokootchke@hotmail.com>
To   statalist <statalist@hsphsun2.harvard.edu>
Subject   RE: st: RE: Econometrics question
Date   Mon, 29 Mar 2010 15:00:22 -0400

Thank you very much, Martin, see below.

----------------------------------------
> From: martin.weiss1@gmx.de
> To: statalist@hsphsun2.harvard.edu
> Subject: st: RE: Econometrics question
> Date: Mon, 29 Mar 2010 20:50:50 +0200
>
>
> <>
>
> The significance also depends on the number of observations in the
> estimation sample, so the "weighted average" need not carry over to the
> standard error estimation:

Right, the fact that the coefficient is strongly significant in the full sample and then insignificant in the two subsamples, is not what surprises me, really. It's the magnitude of the coefficient in the full sample estimation not being between the two coefficients obtained from the subsamples what I find odd...

I don't know if it has anything to do with the country fixed effects... although even in that case, I don't know why that would make things different...

Adrian


>
> ***
> sysuse auto, clear
> reg price weight length
> est store full
> reg price weight length in 1/`=_N/2'
> est store firsthalf
> reg price weight length in `=_N/2+1'/l
> est store secondhalf
> estimates table full firsthalf secondhalf, se style(oneline)
> ***
>
>
> HTH
> Martin
>
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of kokootchke
> Sent: Montag, 29. März 2010 20:39
> To: statalist
> Subject: st: Econometrics question
>
> Dear Stata users,
>
> I have a basic econometric question and I'm hoping you can help me out. I am
> running a regression of bond spreads on various variables denoting domestic
> economic conditions, and country fixed effects; I'm clustering my standard
> errors by quarter, e.g.
>
> xi: regress LogSpread GDPgrowth DebtToGDP i.country, cluster(time)
>
> I have quarterly data for 40 different countries, although it's a very
> unbalanced panel because the spread of the bond is for new bond issues and a
> lot of countries don't issue new bonds every quarter. So, the data would
> look something like this:
>
> Country   Time   Spread GDPgrowth
> Argentina 1991q1 400    3.0
> Argentina 1994q4 450    2.5
> Argentina 2001q3 800    0.7
> Brazil    1993q2 ...
> Brazil    1993q4 ...
> Brazil    1994q1 ...
> Colombia ...
> ...
>
> When I run a simple regression like the one above for the full sample, I
> obtain a coefficient for GDPgrowth of -0.073***
>
> Then if I run this same regression for two separate subsamples for the years
> 1991-1997 and 1998-2006, my coefficients for GDPgrowth are -0.056 and 0.009,
> both insignificant.
>
> In my experience, the full sample coefficient would in general be some sort
> of weighted average of the two coefficients obtained from subsample
> regressions. So, I don't understand why this is not the case here...
>
> The number of observations in the two subsamples add up to the number of
> observations in the full sample estimations.
>
> Any ideas?
>
> Thanks!
> Adrian
>
>
>
>
>
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