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st: Re: RE: Re: xtivreg2


From   "Zou Hong" <[email protected]>
To   <[email protected]>
Subject   st: Re: RE: Re: xtivreg2
Date   Wed, 24 Jan 2007 10:05:31 +0800

sorry, one typo in my previous message.

Dear Mark,


Many thanks for the reply.

I wonder why when I used STATA run a FE model, these "singletons" are were NOT
droped out, the total number of observations reported by STATA includes
those 214 "singletons".

Cheers
Joe


----- Original Message ----- From: "Schaffer, Mark E" <[email protected]>
To: <[email protected]>
Sent: Wednesday, January 24, 2007 9:20 AM
Subject: st: RE: Re: xtivreg2



Joe,

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Zou Hong
Sent: 23 January 2007 10:08
To: [email protected]
Subject: st: Re: xtivreg2

Dear Kit,

Many thanks for your kind suggestion.
I have installed xtivreg2 and run the test as follows.

ttset code year
xtivreg2 y1 x1 x2 x3 (y2 = x4 x5), fe robust endog(y2)

I am suspicious that y2 is endogenous to y1 and want to test
this using a fixed-effect estimation with robust standard
errors. Is the above setup correct?

Can I claim that the above conducted the DWH test using a
fixed-effect estimation with roubt standard errors?
Yes, but your terminology isn't quite right.  The C test (or GMM
distance test) is more general than the DWH test.

Having run the models, I found:

Warning - singleton groups detected.  214 observation(s) not used.
Regarding your question about singletons - these are groups which have
only one member.  In a fixed effects estimation, they drop out
completely.  Put another way, if you dropped these observations and
re-ran your fixed effects estimation, your estimates would be exactly
the same.  It's easy to see why - the fixed effects estimator explains
the "within-group" variation, and when a group has 1 member, there is no
"within-group" variation to explain.

HTH,
Mark


FIXED EFFECTS ESTIMATION
------------------------
Number of groups =       492                    Obs per group: min =
2
                                                               avg =
3.7
                                                               max =
7

(regression output here)
Test statistic(s) not robust
--------------------------------------------------------------
----------------
Cragg-Donald F statistic (weak identification test):
1.907
Stock-Yogo weak ID test critical values:  5% maximal IV relative bias
13.91
                            10% maximal IV relative bias     9.08
                            20% maximal IV relative bias     6.46
                            30% maximal IV relative bias     5.39
                            10% maximal IV size             22.30
                            15% maximal IV size             12.83
                            20% maximal IV size              9.54
                            25% maximal IV size              7.80
Test statistic(s) not robust
Source: Stock-Yogo (2005).  Reproduced by permission.
---------------------------------------------------------Hanse
n J statistic
(overidentification test of all instruments):         3.738
         Chi-sq(2) P-val =    0.1543
-endog- option:

Endogeneity test of endogenous regressors:
0.308
                 Chi-sq(1) P-val =    0.5786
Regressors tested:    y2

what is the meaning of "singleton groups" and how to deal with it?

Thanks a lot
Joe

----- Original Message -----
From: "Kit Baum" <[email protected]>
To: <[email protected]>
Sent: Tuesday, January 23, 2007 11:17 AM
Subject: st: re: ivreg2 update and fixed-effect estimator


> Joe said
>
> 1. where to get the latest version of ivreg2? I always
found it  difficult
> to identify the version of an ado file from the internet.
The one I  found
> from the net is version 02.1.14. But searched from the web,
the latest
 version seems to be 2.1.18. How to update the files if
ivreg2 is always
installed
>
> 2. Under ivreg2, how to test the exogeneity of a regressor under a
> fixed-effect (or random-effects) estimator?
>
> 3. how to request a DWH test using a robust standard error?
>
>
>
> 1. The latest version of ivreg2 (or of just about any user-authored
> software) is available using the ssc or adoupdate commands.
It is  always
> straightforward to check the version number: ssc type
ivreg2.ado will
> display it, as will "which ivreg2" after installation.
>
> 2. You need to use xtivreg2 (a 'wrapper' for ivreg2, also
available  from
> ssc) and the orthog() or endog() option. The help file
explains  them.
>
> 3. The last paragraph of Section 5 of Baum, Schaffer,
Stillman, SJ 3 (1)
> [also available in preprint form as BC WP 545] speaks to
this  point. A
> robust DWH test is available with orthog() or the newer
option endog().
> endog() is not described in that paper, but is  described
in the help
> file. A followup paper describing these  additional features is in
> preparation.
>
> Kit
>
> Kit Baum, Boston College Economics
> http://ideas.repec.org/e/pba1.html
> An Introduction to Modern Econometrics Using Stata:
> http://www.stata-press.com/books/imeus.html
>
>
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>


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