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From |
"Burak Darbaz" <infinisafricae@hotmail.com> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: Re: restricting sum of coefficients in IV |

Date |
Sat, 7 Aug 2010 19:52:09 +0100 |

Nope, I made a mistake typing out the instruments, the result is still slightly different but not that off now. Thanks a lot for the help. Burak -----Original Message----- From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Christopher Baum Sent: 07 August 2010 09:07 To: statalist@hsphsun2.harvard.edu Subject: st: Re: restricting sum of coefficients in IV <> On Aug 7, 2010, at 2:33 AM, Burak wrote: > First, in the original specification (unrestricted), I get the following > coefficients > > F.gnd = .5361618 > L.gnd = .4614466 > > (they are all significant), so they already sum up to approximately one. > > Then, when I try to restrict it by using the approach you have shown (D.gnd > on the left hand side and F.gnd-L.gnd on the right hand side), I get > a coefficient FLgnd = .4480393 (significant) > > Isn't this a bit off? I mean, it drops from .53 to .44 even though the > unrestricted model's coefficients almost sum up to one. > > Besides that, I couldn't manage to use lincom to get the coeff on L.gnd, > however, shouldnt 1-(FLgnd's coefficient) should be enough to get it? Well, with that restriction imposed, you are solving a different optimization problem. For instance, the correlation of FLgnd with the instruments would certainly be different than that of F.gnd. So it doesn't surprise me. You should be able to do lincom 1 - FLgnd after estimation to get the estimate of the other coefficient. Kit Kit Baum | Boston College Economics & DIW Berlin | http://ideas.repec.org/e/pba1.html An Introduction to Stata Programming | http://www.stata-press.com/books/isp.html An Introduction to Modern Econometrics Using Stata | http://www.stata-press.com/books/imeus.html * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: Re: restricting sum of coefficients in IV***From:*Christopher Baum <kit.baum@bc.edu>

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