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st: RE: xtoverid error: internal reestimation of eqn differs from original


From   SEZER ALCAN <[email protected]>
To   "[email protected]" <[email protected]>
Subject   st: RE: xtoverid error: internal reestimation of eqn differs from original
Date   Tue, 28 Jan 2014 16:10:47 +0000

I copied original estimation and xtoverid, noi results. As you can see same number of observation is used and coefficients are not substantially different. You may see it below. 

I very much appreciate your comments
Regards,
Sezer Alcan



xtivreg y $xvars (sahgd = hlthlm), re 

G2SLS random-effects IV regression              Number of obs      =     10051
Group variable: FKIMLIK                         Number of groups   =      3784

R-sq:  within  = 0.0479                         Obs per group: min =         2
       between = 0.5865                                        avg =       2.7
       overall = 0.5116                                        max =         4

                                                Wald chi2(26)      =   5525.18
corr(u_i, X)       = 0 (assumed)                Prob > chi2        =    0.0000

------------------------------------------------------------------------------
           y |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       sahgd |   .0681581   .0329966     2.07   0.039      .003486    .1328303
         age |   .0841604   .0058326    14.43   0.000     .0727286    .0955922
        age2 |  -.0008967   .0000755   -11.88   0.000    -.0010446   -.0007488
         wed |    .122449   .0210754     5.81   0.000      .081142     .163756
       illit |  -.1637081   .0654399    -2.50   0.012     -.291968   -.0354482
     secprim |   .0974501   .0232707     4.19   0.000     .0518404    .1430599
     highsch |   .2458178   .0269148     9.13   0.000     .1930658    .2985698
     techigh |   .2928797   .0262241    11.17   0.000     .2414815     .344278
        univ |   .5371905   .0325742    16.49   0.000     .4733463    .6010348
   nutriengh |   .1259238   .0120452    10.45   0.000     .1023156    .1495319
   socsecprb |   .2143147   .0183127    11.70   0.000     .1784225    .2502069
        prof |   .4363263   .0348374    12.52   0.000     .3680462    .5046064
       manag |   .4134413   .0367269    11.26   0.000     .3414578    .4854248
       craft |  -.0143766   .0231956    -0.62   0.535    -.0598391    .0310859
      machop |  -.0575744     .02341    -2.46   0.014    -.1034571   -.0116917
      unskll |  -.1693637   .0235825    -7.18   0.000    -.2155845   -.1231429
 nutriunskll |  -.0274815   .0302797    -0.91   0.364    -.0868286    .0318655
     sector3 |   .0279124    .019475     1.43   0.152    -.0102579    .0660826
     sector5 |  -.0255151   .0249776    -1.02   0.307    -.0744704    .0234402
     sector6 |  -.1065776   .0218064    -4.89   0.000    -.1493174   -.0638379
  firmsize10 |  -.0530375   .0196092    -2.70   0.007    -.0914708   -.0146041
firmsize2049 |   .0864132    .023699     3.65   0.000      .039964    .1328624
 firmsize50p |   .1883012   .0214952     8.76   0.000     .1461715    .2304309
        perm |   .1811101    .020985     8.63   0.000     .1399803    .2222399
      yr2008 |  -.1080605   .0104045   -10.39   0.000     -.128453   -.0876681
      yr2009 |  -.0215809   .0089087    -2.42   0.015    -.0390417   -.0041201
       _cons |   -1.27803   .1101712   -11.60   0.000    -1.493962   -1.062099
-------------+----------------------------------------------------------------
     sigma_u |  .40067359
     sigma_e |  .36180592
         rho |  .55084324   (fraction of variance due to u_i)
------------------------------------------------------------------------------
Instrumented:   sahgd
Instruments:    age age2 wed illit secprim highsch techigh univ nutriengh
                socsecprb prof manag craft machop unskll nutriunskll sector3
                sector5 sector6 firmsize10 firmsize2049 firmsize50p perm
                yr2008 yr2009 hlthlm
------------------------------------------------------------------------------

. xtoverid
xtoverid error: internal reestimation of eqn differs from original
r(198);

. xtoverid, noi

First-stage regressions
-----------------------

First-stage regression of __00000I:

OLS estimation
--------------

Estimates efficient for homoskedasticity only
Statistics consistent for homoskedasticity only

                                                      Number of obs =    10051
                                                      F( 27, 10024) =   774.81
                                                      Prob > F      =   0.0000
Total (centered) SS     =  948.7104765                Centered R2   =   0.2241
Total (uncentered) SS   =  2272.334237                Uncentered R2 =   0.6761
Residual SS             =  736.1052268                Root MSE      =     .271

------------------------------------------------------------------------------
    __00000I |      Coef.   Std. Err.      t    P>|t|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
    __00000O |  -.0012507    .003727    -0.34   0.737    -.0085564    .0060551
    __00000R |  -.0000673   .0000483    -1.39   0.164     -.000162    .0000275
    __00000U |  -.0085974   .0141249    -0.61   0.543     -.036285    .0190902
    __00000X |   -.210671    .042279    -4.98   0.000    -.2935463   -.1277956
    __000010 |   .0274273   .0149386     1.84   0.066    -.0018553    .0567099
    __000013 |   .0184523   .0177786     1.04   0.299    -.0163974    .0533019
    __000016 |   .0513269     .01727     2.97   0.003     .0174743    .0851794
    __000019 |   .0530563   .0218709     2.43   0.015      .010185    .0959275
    __00001C |   .0344548   .0085254     4.04   0.000     .0177433    .0511663
    __00001F |   .0304538   .0124402     2.45   0.014     .0060685    .0548392
    __00001I |  -.0071152   .0235747    -0.30   0.763    -.0533263    .0390959
    __00001L |   .0168858   .0254501     0.66   0.507    -.0330014    .0667731
    __00001O |  -.0067492    .015419    -0.44   0.662    -.0369735    .0234751
    __00001R |  -.0004078     .01575    -0.03   0.979     -.031281    .0304653
    __00001U |  -.0480332   .0157943    -3.04   0.002    -.0789933   -.0170732
    __00001X |   .0131181   .0212184     0.62   0.536    -.0284742    .0547104
    __000020 |  -.0202486   .0132233    -1.53   0.126    -.0461689    .0056717
    __000023 |   .0242722    .016993     1.43   0.153    -.0090374    .0575819
    __000026 |  -.0206897   .0145767    -1.42   0.156     -.049263    .0078835
    __000029 |   .0081375   .0134997     0.60   0.547    -.0183246    .0345997
    __00002C |   .0016234   .0162664     0.10   0.921     -.030262    .0335087
    __00002F |  -.0160256   .0147908    -1.08   0.279    -.0450186    .0129673
    __00002I |   .0114303   .0143138     0.80   0.425    -.0166277    .0394883
    __00002L |   .0069627   .0073903     0.94   0.346    -.0075237    .0214491
    __00002O |  -.0058741   .0063412    -0.93   0.354    -.0183042     .006556
    __00000E |   .9547274   .0680486    14.03   0.000     .8213384    1.088116
    __00000L |  -.4283008   .0097704   -43.84   0.000    -.4474527   -.4091489
------------------------------------------------------------------------------
Included instruments: __00000O __00000R __00000U __00000X __000010 __000013
                      __000016 __000019 __00001C __00001F __00001I __00001L
                      __00001O __00001R __00001U __00001X __000020 __000023
                      __000026 __000029 __00002C __00002F __00002I __00002L
                      __00002O __00000E __00000L
------------------------------------------------------------------------------
F test of excluded instruments:
  F(  1, 10024) =  1921.65
  Prob > F      =   0.0000
Angrist-Pischke multivariate F test of excluded instruments:
  F(  1, 10024) =  1921.65
  Prob > F      =   0.0000



Summary results for first-stage regressions
-------------------------------------------

                                           (Underid)            (Weak id)
Variable     | F(  1, 10024)  P-val | AP Chi-sq(  1) P-val | AP F(  1, 10024)
__00000I     |    1921.65    0.0000 |     1926.83   0.0000 |     1921.65

Stock-Yogo weak ID test critical values for single endogenous regressor:
                                   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.

Underidentification test
Ho: matrix of reduced form coefficients has rank=K1-1 (underidentified)
Ha: matrix has rank=K1 (identified)
Anderson canon. corr. LM statistic       Chi-sq(1)=1616.87  P-val=0.0000

Weak identification test
Ho: equation is weakly identified
Cragg-Donald Wald F statistic                                    1921.65

Stock-Yogo weak ID test critical values for K1=1 and L1=1:
                                   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.

Weak-instrument-robust inference
Tests of joint significance of endogenous regressors B1 in main equation
Ho: B1=0 and orthogonality conditions are valid
Anderson-Rubin Wald test           F(1,10024)=     7.17     P-val=0.0074
Anderson-Rubin Wald test           Chi-sq(1)=      7.19     P-val=0.0073
Stock-Wright LM S statistic        Chi-sq(1)=      7.19     P-val=0.0073

Number of observations               N  =      10051
Number of regressors                 K  =         27
Number of endogenous regressors      K1 =          1
Number of instruments                L  =         27
Number of excluded instruments       L1 =          1

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

Estimates efficient for homoskedasticity only
Statistics consistent for homoskedasticity only

                                                      Number of obs =    10051
                                                      F( 27, 10024) =   927.71
                                                      Prob > F      =   0.0000
Total (centered) SS     =  2432.217133                Centered R2   =   0.3602
Total (uncentered) SS   =  5444.007778                Uncentered R2 =   0.7142
Residual SS             =  1556.070469                Root MSE      =    .3935

------------------------------------------------------------------------------
    __00000G |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
    __00000I |   .0888147   .0331225     2.68   0.007     .0238959    .1537336
    __00000O |   .0757184   .0054114    13.99   0.000     .0651122    .0863246
    __00000R |  -.0008138   .0000703   -11.58   0.000    -.0009515    -.000676
    __00000U |   .1304926   .0205185     6.36   0.000      .090277    .1707081
    __00000X |  -.1801946   .0620044    -2.91   0.004    -.3017211   -.0586681
    __000010 |   .1117898   .0217153     5.15   0.000     .0692286     .154351
    __000013 |   .2030786   .0258334     7.86   0.000      .152446    .2537111
    __000016 |   .2834297   .0251911    11.25   0.000      .234056    .3328033
    __000019 |   .5128589   .0318645    16.09   0.000     .4504056    .5753122
    __00001C |   .1253982   .0124417    10.08   0.000     .1010129    .1497835
    __00001F |   .2136176   .0180921    11.81   0.000     .1781577    .2490774
    __00001I |   .4131903   .0342317    12.07   0.000     .3460974    .4802832
    __00001L |    .436081   .0369653    11.80   0.000     .3636303    .5085317
    __00001O |   -.019046   .0223885    -0.85   0.395    -.0629268    .0248347
    __00001R |  -.0736599   .0228685    -3.22   0.001    -.1184813   -.0288385
    __00001U |  -.1782438   .0229984    -7.75   0.000    -.2233199   -.1331676
    __00001X |  -.0256015   .0308117    -0.83   0.406    -.0859914    .0347884
    __000020 |   .0228741   .0192233     1.19   0.234    -.0148028     .060551
    __000023 |  -.0349952   .0246815    -1.42   0.156    -.0833701    .0133797
    __000026 |  -.1084179   .0211765    -5.12   0.000     -.149923   -.0669128
    __000029 |  -.0628365   .0196054    -3.21   0.001    -.1012624   -.0244106
    __00002C |   .0772072   .0236188     3.27   0.001     .0309153    .1234991
    __00002F |   .1776297   .0214788     8.27   0.000     .1355321    .2197273
    __00002I |   .1943209   .0207961     9.34   0.000     .1535613    .2350805
    __00002L |  -.1077913   .0107296   -10.05   0.000     -.128821   -.0867616
    __00002O |  -.0214963   .0092137    -2.33   0.020    -.0395548   -.0034378
    __00000E |  -1.095742   .1031156   -10.63   0.000    -1.297845   -.8936388
------------------------------------------------------------------------------
Underidentification test (Anderson canon. corr. LM statistic):        1616.868
                                                   Chi-sq(1) P-val =    0.0000
------------------------------------------------------------------------------
Weak identification test (Cragg-Donald Wald F statistic):             1921.654
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.
------------------------------------------------------------------------------
Sargan statistic (overidentification test of all instruments):           0.000
                                                 (equation exactly identified)
------------------------------------------------------------------------------
Instrumented:         __00000I
Included instruments: __00000O __00000R __00000U __00000X __000010 __000013
                      __000016 __000019 __00001C __00001F __00001I __00001L
                      __00001O __00001R __00001U __00001X __000020 __000023
                      __000026 __000029 __00002C __00002F __00002I __00002L
                      __00002O __00000E
Excluded instruments: __00000L
------------------------------------------------------------------------------
xtoverid error: internal reestimation of eqn differs from original
r(198);

________________________________________
From: [email protected] [[email protected]] on behalf of Schaffer, Mark E [[email protected]]
Sent: Tuesday, January 28, 2014 5:51 PM
To: [email protected]
Subject: st: RE: RE: xtoverid error: internal reestimation of eqn differs from original

Sezer,

> -----Original Message-----
> From: [email protected] [mailto:owner-
> [email protected]] On Behalf Of SEZER ALCAN
> Sent: 28 January 2014 15:42
> To: [email protected]
> Subject: st: RE: xtoverid error: internal reestimation of eqn differs from
> original
>
> Dr Schaffer,
>  Although xtoverid gives error,  xtoverid, noi still reports under identification
> test, weak identification test and sargan statistics.
> What if internal estimation results by ivreg2  after xtoverid,noi  command
> does show any collinearity (no regressors are dropped) is it possible to rely
> on these test results?

They should be OK, but because they don't match the original estimation you can't use them with the original estimation results - they don't apply.

In what respects to the original results differ from the xtoverid results?  Do they use the same number of observations?  Same number of coefficients reported?  Are the coefficients very slightly different or substantially different?  Are the same variables being treated as endogenous?  (One possibility is that collinearity with the excluded instruments is causing an endogenous regressor to be treated as if it is exogenous.)

If the results aren't confidential, you can post them here and we can try to work out what is going on.

--Mark

> Regards,
> Sezer Alcan
> ________________________________________
> From: [email protected] [owner-
> [email protected]] on behalf of Schaffer, Mark E
> [[email protected]]
> Sent: Wednesday, January 22, 2014 10:16 PM
> To: [email protected]
> Subject: st: RE: xtoverid error: internal reestimation of eqn differs from
> original
>
> Sezer,
>
> > -----Original Message-----
> > From: [email protected] [mailto:owner-
> > [email protected]] On Behalf Of SEZER ALCAN
> > Sent: 22 January 2014 18:11
> > To: [email protected]
> > Subject: st: xtoverid error: internal reestimation of eqn differs from
> > original
> >
> > When I use xtoverid command in stata after estimation by xthtaylor or
> xtivreg
> > re /xtivreg fe,    I get "xtoverid error: internal reestimation of eqn differs
> from
> > original".  I read all replies under this subject; Dr Schaffer says
> > that it may be because of collinearity. However when I execute "
> > xtoverid, noisily " I do not detect any collinearity.
>
> Strictly speaking, my suggestion isn't that collinearity is causing the internal
> reestimation to vary from the original estimation.  Rather, it's how Stata's
> official xthtaylor or xtivreg handles the collinearity vs. how the internal
> reestimation by xtoverid (using ivreg2) handles it.
>
> If there is perfect collinearity, Stata estimators will typically drop enough
> regressors or instruments to make the collinearity go away.  But which of the
> collinear regressors get dropped can vary.  And this can make the estimated
> coefficients vary even though, in some sense, it's the same model.
>
> If you look at the internal estimation results by ivreg2 that xtoverid,noi
> reports, you should see at the bottom of the main output whether ivreg2 is
> dropping any collinear regressors or instruments.  You won't be able to easily
> map the ones that are being dropped to your dataset, because xtoverid uses
> temporary variables, but it should at least be a good clue to what is going on.
>
> HTH,
> Mark
>
> >
> > I was wondering if this problem was due to unbalanced nature of the
> > panel I was using. If so what other  test can be executed to test over
> > identification restrictions in an unbalanced panel.
> > If collinearity isn't the problem of the error, can  xtoverid, noi
> > test results be trusted ?
> >
> >
> > I work wiht Stata 12 and latest version of xtoverid is installed.
> >
> > Thanks all in advance,
> > Sezer Alcan
> > *
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>
>
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-----
Sunday Times Scottish University of the Year 2011-2013
Top in the UK for student experience
Fourth university in the UK and top in Scotland (National Student Survey 2012)


We invite research leaders and ambitious early career researchers to
join us in leading and driving research in key inter-disciplinary themes.
Please see www.hw.ac.uk/researchleaders for further information and how
to apply.

Heriot-Watt University is a Scottish charity
registered under charity number SC000278.


*
*   For searches and help try:
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