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Re: st: Using ivregress when the endogenous variable is used in an interaction term in the main regression
From
Tirthankar Chakravarty <[email protected]>
To
[email protected]
Subject
Re: st: Using ivregress when the endogenous variable is used in an interaction term in the main regression
Date
Wed, 21 Dec 2011 04:44:14 -0800
Not quite; here is the recommended procedure (I am assuming that you
have the main effect of the endogenous variable in there as in Y =
a*X2 + b*X1*X2 + controls):
1) -regress- X2 on _all_ instruments (included exogenous controls and
excluded instruments) and get predictions X2hat.
2) Form interactions of X2hat with the exogenous variable X1, that is, X2hat*X1.
3) -ivregress- instrumenting for X2 and X2*X1 using X2hat and X2hat*X1.
Note that there is distinction between two calls to -regress- and
using -ivregress- for 3).
T
On Wed, Dec 21, 2011 at 3:43 AM, Nick Kohn <[email protected]> wrote:
> Thanks for the reply.
>
> My simplified model is (X2 is endogenous):
> Y = b*X1*X2 + controls
>
> In regards to the third option you suggest, would I do the following?
>
> 1) First stage regression to get X2hat using the instrument Z
> 2) Run the first stage again but use X1*X2hat as the instrument for
> X1*X2 (so Z is no longer used)
> 3) Run the second stage using (X1*X2)hat (so the whole product is
> fitted from step 2))
>
> On Wed, Dec 21, 2011 at 12:24 PM, Tirthankar Chakravarty
> <[email protected]> wrote:
>> You can see my previous reply to a similar question here:
>> http://www.stata.com/statalist/archive/2011-08/msg01496.html
>>
>> T
>>
>> On Wed, Dec 21, 2011 at 2:24 AM, Nick Kohn <[email protected]> wrote:
>>> Hi,
>>>
>>> I have a specification in which the endogenous variable is interacted
>>> with an exogenous variable. Since I cannot multiply the variables
>>> directly in the regression, I create a new variable. In ivregress it
>>> makes no sense to use the entire interaction term as the endogenous
>>> variable.
>>>
>>> I can do the first stage manually (and then use the fitted value in
>>> the main regression), however, from what I remember the standard
>>> errors will be wrong when doing it manually.
>>>
>>> Is there a way to overcome this?
>>>
>>> Thanks
>>> *
>>> * 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/
>>
>>
>>
>> --
>> Tirthankar Chakravarty
>> [email protected]
>> [email protected]
>>
>> *
>> * 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/
--
Tirthankar Chakravarty
[email protected]
[email protected]
*
* 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/