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From |
Sun Yutao <yutao.sun.statalist@outlook.com> |

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

Subject |
RE: st: OLS and IV have opposite sign |

Date |
Mon, 15 Oct 2012 22:40:54 +0200 |

You mean you get the same value but different signs? -----Original Message----- From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Shikha Sinha Sent: Monday, October 15, 2012 10:33 PM To: statalist@hsphsun2.harvard.edu Subject: Re: st: OLS and IV have opposite sign I am estimating the effect of family size (no of children) on probability of work by mother. The endogenous variable is no of children and I instrument this by gender of first born. If the first child is female then family size should be greater. I understand that IV correct the bias and OLS coeff may be upward or downward biased. One can sign the bias (+) or (-) by examining the correlation between the omited variable and endogenous, but What I do not understand why the sign would change and what determines the opposite sign. I get a negative OLS while a positive IV coeff. Thanks, Shikha On Mon, Oct 15, 2012 at 1:11 PM, Austin Nichols <austinnichols@gmail.com> wrote: > 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? > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/faqs/resources/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/faqs/resources/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/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

**References**:**st: OLS and IV have opposite sign***From:*Shikha Sinha <shikha.sinha414@gmail.com>

**Re: st: OLS and IV have opposite sign***From:*Austin Nichols <austinnichols@gmail.com>

**Re: st: OLS and IV have opposite sign***From:*Shikha Sinha <shikha.sinha414@gmail.com>

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