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RE: st: RE: RE: xtivreg2 -- Instruments dropped


From   DE SOUZA Eric <eric.de_souza@coleurope.eu>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   RE: st: RE: RE: xtivreg2 -- Instruments dropped
Date   Sun, 16 Jan 2011 15:37:38 +0100

So the space before the comma was the reason I couldn't get it to run this time. I saw the error message but then had to move on something else.

Eric


Eric de Souza
College of Europe
Brugge (Bruges), Belgium
http://www.coleurope.eu



-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Schaffer, Mark E
Sent: 16 January 2011 15:30
To: statalist@hsphsun2.harvard.edu
Subject: RE: st: RE: RE: xtivreg2 -- Instruments dropped

Ivan,

I used your corrected dataset, and made some progress in tracking down the problem, but there are still aspects I don't understand.

1.  Easy part: to identify your versions of xtivreg2, ivreg2, xtivreg, etc., you use the -which- command.  It's best to use the -all- option with it, in case there are multiple versions lurking on your machine.  For example,

. which xtivreg, all

C:\Program Files\Stata11\ado\updates\x\xtivreg.ado
*! version 1.5.9  11nov2009

C:\Program Files\Stata11\ado\base\x\xtivreg.ado
*! version 1.5.7  17jun2009

NB: The dulpicate versions above aren't a problem for an official program like -xtivreg-.  When you update your Stata and a do file gets updated, the update goes in the updates folder and the original stays in the base folder.

2.  I can't run your example, using either -xtivreg2- or official -xtivreg-.  The reason is a bug, or perhaps "inflexibility", in the parsing done by -xtivreg2- and -xtivreg-.  It is very simple: if you use a space between the end of an -if- statement and the comma, both -xtivreg2- and -xtivreg- complain in a very uninformative way:

First, -xtivreg2-:

. xi: xtivreg2 xrdr_ln revtr_ln mktbook_mm ebitdar_ln     ///
>         taxcred (L.utsa = L.govr_r) i.year ///
>         if xrdr_count >= 6  , fe cluster(state_sic)
i.year            _Iyear_1976-2006    (naturally coded; _Iyear_1976 omitted)
6  invalid name
r(198);

end of do-file

r(198);

Now official -xtivreg-:

. xi: xtivreg xrdr_ln revtr_ln mktbook_mm ebitdar_ln      ///
>         taxcred (L.utsa = L.govr_r) i.year ///
>         if xrdr_count >= 6  , fe cluster(state_sic)
i.year            _Iyear_1976-2006    (naturally coded; _Iyear_1976 omitted)
6  invalid name
r(198);

end of do-file

r(198);

But delete the spaces between 6 and the comma, and it works:

. xi: xtivreg2 xrdr_ln revtr_ln mktbook_mm ebitdar_ln     ///
>         taxcred (L.utsa = L.govr_r) i.year ///
>         if xrdr_count >= 6, fe cluster(state_sic)
i.year            _Iyear_1976-2006    (naturally coded; _Iyear_1976 omitted)
Warning - singleton groups detected.  295 observation(s) not used.
Warning - collinearities detected
Vars dropped:  _Iyear_2006

FIXED EFFECTS ESTIMATION
------------------------
Number of groups =      3198                    Obs per group: min =         2
                                                               avg =       8.5
                                                               max =        30

IV (2SLS) estimation
--------------------

Estimates efficient for homoskedasticity only Statistics robust to heteroskedasticity and clustering on state_sic

Number of clusters (state_sic) =   1471               Number of obs =    27044
                                                      F( 34,  1470) =     3.85
                                                      Prob > F      =   0.0000
Total (centered) SS     =  251.0415486                Centered R2   =   0.2476
Total (uncentered) SS   =  251.0415486                Uncentered R2 =   0.2476
Residual SS             =  188.8924922                Root MSE      =     .089

------------------------------------------------------------------------------
             |               Robust
     xrdr_ln |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------
-------------+------
        utsa |
         L1. |   .0174583   .0902999     0.19   0.847    -.1595263    .1944429
             |
    revtr_ln |   .1265504   .0205411     6.16   0.000     .0862907    .1668102
  mktbook_mm |   .0149745   .3796314     0.04   0.969    -.7290894    .7590385
  ebitdar_ln |   .0408917   .0159209     2.57   0.010     .0096873    .0720961
     taxcred |  -.1079932   .5174864    -0.21   0.835    -1.122248    .9062615
 _Iyear_1977 |  -.0313348   .0448701    -0.70   0.485    -.1192785     .056609
...
<output edited for brevity>
...
 _Iyear_2005 |  -.0105457   .0033898    -3.11   0.002    -.0171896   -.0039017
------------------------------------------------------------------------------
Underidentification test (Kleibergen-Paap rk LM statistic):             46.831
                                                   Chi-sq(1) P-val =    0.0000
------------------------------------------------------------------------------
Weak identification test (Cragg-Donald Wald F statistic):              202.397
                         (Kleibergen-Paap rk Wald F statistic):         53.412
Stock-Yogo weak ID test critical values: 10% maximal IV size             16.38
                                         15% maximal IV size              8.96
                                         20% maximal IV size              6.66
                                         25% maximal IV size              5.53
Source: Stock-Yogo (2005).  Reproduced by permission.
NB: Critical values are for Cragg-Donald F statistic and i.i.d. errors.
------------------------------------------------------------------------------
Hansen J statistic (overidentification test of all instruments):         0.000
                                                 (equation exactly identified)
------------------------------------------------------------------------------
Instrumented:         L.utsa
Included instruments: revtr_ln mktbook_mm ebitdar_ln taxcred _Iyear_1977 ...
<output edited for brevity>
...                      _Iyear_2002 _Iyear_2003 _Iyear_2004 _Iyear_2005
Excluded instruments: L.govr_r
Dropped collinear:    _Iyear_2006
------------------------------------------------------------------------------

3.  I still don't understand what you mean when you say

> IP: I meant instruments -- in the sense that I used different 
> instruments in various specifications, and each one was dropped.

I'm pretty sure you don't mean that -xtivreg2- drops every excluded instrument but still reports a coefficient for an endogenous regressor!  But then, what do you mean?

But maybe it doesn't matter if simply eliminating the spaces between 6 and the comma solves your problem.

Best wishes,
Mark

> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Ivan Png
> Sent: 16 January 2011 03:25
> To: statalist@hsphsun2.harvard.edu
> Subject: Re: st: RE: RE: xtivreg2 -- Instruments dropped
> 
> Sorry, Mark.  I've updated the data-set.
> 
> On Sat, Jan 15, 2011 at 10:29 PM, Schaffer, Mark E 
> <M.E.Schaffer@hw.ac.uk> wrote:
> > Ivan,
> >
> > I had the same problem as Eric.  And there must be
> something else wrong, since there's only one instrument listed 
> (L.govr_r) and you refer to "instruments".
> >
> 
> IP: I meant instruments -- in the sense that I used different 
> instruments in various specifications, and each one was dropped.
> 
> > Did xtivreg2 report collinearities among your instruments
> as a reason for dropping some?  Did xtivreg?  If so, were the dropped 
> variables the same?
> 
> IP; Neither reported collinearities.
> 
> > You might also want to compare the first-stage regressions
> of xtivreg2 and xtivreg.
> >
> > Oh, and tell us which versions of xtivreg2, xtivreg and
> Stata you are using.
> 
> IP: Stata/IC 10.1.  Sorry, please advise how to identify version of
> xtivreg2 and xtivreg
> 
> 
> > --Mark
> >
> >> -----Original Message-----
> >> From: owner-statalist@hsphsun2.harvard.edu
> >> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of
> DE SOUZA
> >> Eric
> >> Sent: 15 January 2011 12:02
> >> To: statalist@hsphsun2.harvard.edu
> >> Subject: st: RE: xtivreg2 -- Instruments dropped
> >>
> >> Check the instruction you have posted:
> >> govr_r does not exist
> >>
> >>
> >>
> >> Eric de Souza
> >> College of Europe
> >> Brugge (Bruges), Belgium
> >> http://www.coleurope.eu
> >>
> >>
> >> -----Original Message-----
> >> From: owner-statalist@hsphsun2.harvard.edu
> >> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Ivan Png
> >> Sent: 15 January 2011 12:43
> >> To: statalist@hsphsun2.harvard.edu
> >> Subject: st: xtivreg2 -- Instruments dropped
> >>
> >> Dear Stata-list:
> >>
> >> I'm having difficulty with xtivreg2
> >>
> >> Each time, the system drops the instruments for the
> variable L.utsa.
> >> utsa is a state-time variable that varies across states
> and times. I
> >> checked the instruments: they are state- and time-varying.
>   I don't
> >> understand why the system drops the instruments.  (I tried xtivreg 
> >> and it works, but I would like to use xtivreg2 so that I can get 
> >> cluster standard errors and the diagnostics for weak instruments).
> >>
> >>
> >> Please help.  Many thanks!
> >>
> >> Data-set:
> >> http://www.comp.nus.edu.sg/~ipng/research/company_wrkg.dta
> >>
> >>
> >> Code:
> >> . xtset gvkey year
> >>
> >> . xi: xtivreg2 xrdr_ln revtr_ln mktbook_mm ebitdar_ln taxcred ///
> >>     (L.utsa = L.govr_r) i.year trend_AL - trend_WY ///
> >>     if xrdr_count >= 6  , fe cluster(state_sic)
> >>
> >>
> >>
> >>
> >> --
> >> Ivan Png
> >> National U of Singapore
> >>
> >>
> >>
> >>
> >> --
> >> Skype: ipng00
> >> T: +65 6516 6807
> >>
> >>
> >>
> >> --
> >> Skype: ipng00
> >> T: +65 6516 6807
> >>
> >> *
> >> *   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/
> >>
> >
> >
> > --
> > Heriot-Watt University is a Scottish charity registered
> under charity
> > number SC000278.
> >
> >
> > *
> > *   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/
> >
> 
> 
> 
> --
> Skype: ipng00
> T: +65 6516 6807
> 
> *
> *   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/
> 


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