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Re: st: OLS and IV have opposite sign


From   Austin Nichols <austinnichols@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: OLS and IV have opposite sign
Date   Mon, 15 Oct 2012 16:11:20 -0400

Shikha Sinha <shikha.sinha414@gmail.com>:
The econometric reason is simple if you believe the exclusion
restriction.  Tell us what the endog var is, what the excluded
instruments are, and someone on the list will provide a (verbal)
description of the bias producing a negative OLS coef estimate
(evidently no longer visible in the consistent IV estimate).  Then
someone else will weigh in on whether the exclusion restriction makes
sense, probably...

On Mon, Oct 15, 2012 at 3:58 PM, Shikha Sinha <shikha.sinha414@gmail.com> wrote:
> Dear all,
>
> I am estimating an Ordinary least square (OLS) and Instrument variable
> (IV) model, however the signs are opposite to each other. The OLS
> coeff is negative, while the IV coeff is positive. Could anyone
> explain what the signs in these two models are different- is there any
> econometric reason for this?
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