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From |
"Schaffer, Mark E" <[email protected]> |

To |
<[email protected]> |

Subject |
st: RE: instrumental variable nomenclature |

Date |
Mon, 25 Aug 2008 20:07:22 +0100 |

```
Al,
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of
> Feiveson, Alan H. (JSC-SK311)
> Sent: 25 August 2008 19:26
> To: [email protected]
> Subject: st: instrumental variable nomenclature
>
> Hi - I am looking for a name/title to describe the following
> simulatenous-equation model:
>
> This starts with a linear regression model Y = X*b + e, but X
> is not observed. However we know X is correlated with an
> observable variable Z, with error term independent of e. So
> at this point, would it be correct to say this is an
> instrumental variable model with Z as an instrument for X?
Not quite. Say the "true model" is
Y = X*b + e
but you estimate
Y = Z*b + u
Z is an imperfect measure of X. Say that
Z = X*a + v
This is the classic measurement error problem. If you had an instrument
for X, you could get a consistent estimate of b using linear IV.
HTH.
Cheers,
Mark
> Furthermore we also observe K = g(X) where g is a step
> function (for example, K follows an ordered probit model with
> X as the latent variable). So to get the nomenclature
> straight, can I say that this is a nonlinear simultaneous
> equation model (one equation for Y given X, and one for K
> given X), with Z as an "instrumental variable for X"?
>
> Of course, how to estimate such a model is another story!
>
> Thanks for whatever suggestions (names or estimation
> approach) you can provide.
>
> Al Feiveson
>
> *
> * For searches and help try:
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> * http://www.ats.ucla.edu/stat/stata/
>
--
Heriot-Watt University is a Scottish charity
registered under charity number SC000278.
*
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```

**Follow-Ups**:**st: RE: RE: instrumental variable nomenclature***From:*"Feiveson, Alan H. (JSC-SK311)" <[email protected]>

**References**:**st: instrumental variable nomenclature***From:*"Feiveson, Alan H. (JSC-SK311)" <[email protected]>

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