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st: How can I interpret the result of xtabond2 ?


From   "Lee, Seung-Won (MU-Student)" <slrgd@mizzou.edu>
To   statalist@hsphsun2.harvard.edu
Subject   st: How can I interpret the result of xtabond2 ?
Date   Mon, 22 Sep 2008 23:18:15 -0500

Dear stata users
 
I'm a just beginner for xtabond2, so I don't know how to interpret the result below especially regarding
 
Arellano-Bond autocorrelation test, Sargan test and Hansen test.
 
I'm not sure but my guess is that it says that there is both AR(1) and AR(2), may be some IVs are correlated with error term.  If my guess is right, then what should I do?
 
Please see my log below and help!!
 
 
 
. xtabond2 dlcapx l1_dlcapx dls l1_xinter4 l1_minter4 y9* y0*, gmm(l1_dlcapx dls) iv(l1_xinter4 l1_minter4 y9* y0*, equation(level)) orth
> ogonal robust twostep
Favoring speed over space. To switch, type or click on mata: mata set matafavor space, perm.
y90 dropped due to collinearity
y91 dropped due to collinearity
y92 dropped due to collinearity
y93 dropped due to collinearity
y94 dropped due to collinearity
y95 dropped due to collinearity
y96 dropped due to collinearity
y97 dropped due to collinearity
y07 dropped due to collinearity
Warning: Two-step estimated covariance matrix of moments is singular.
  Using a generalized inverse to calculate optimal weighting matrix for two-step estimation.
  Difference-in-Sargan statistics may be negative.
Dynamic panel-data estimation, two-step system GMM
------------------------------------------------------------------------------
Group variable: gvkey                           Number of obs      =      3607
Time variable : year                            Number of groups   =       874
Number of instruments = 218                     Obs per group: min =         2
Wald chi2(13) =    211.52                                      avg =      4.13
Prob > chi2   =     0.000                                      max =        10
------------------------------------------------------------------------------
             |              Corrected
      dlcapx |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
   l1_dlcapx |  -.2007464   .0302184    -6.64   0.000    -.2599734   -.1415195
         dls |   .6778161   .0993139     6.82   0.000     .4831644    .8724677
  l1_xinter4 |   -2.53827    1.47796    -1.72   0.086     -5.43502    .3584791
  l1_minter4 |   17.70894   5.754314     3.08   0.002     6.430696    28.98719
         y98 |  -.0185858   .2891494    -0.06   0.949    -.5853082    .5481365
         y99 |  -.0792788   .2839134    -0.28   0.780    -.6357388    .4771813
         y00 |  -.0249017   .2810219    -0.09   0.929    -.5756945    .5258911
         y01 |  -.2103614   .2918474    -0.72   0.471    -.7823718     .361649
         y02 |  -.2527464   .2846071    -0.89   0.375    -.8105661    .3050734
         y03 |  -.0863709   .2797089    -0.31   0.757    -.6345903    .4618485
         y04 |   .2565646   .2892443     0.89   0.375    -.3103438    .8234729
         y05 |   .1678996   .2790313     0.60   0.547    -.3789918    .7147909
         y06 |   .0993331   .2821207     0.35   0.725    -.4536133    .6522794
       _cons |  -.0553731    .277753    -0.20   0.842     -.599759    .4890129
------------------------------------------------------------------------------
Instruments for orthogonal deviations equation
  GMM-type (missing=0, separate instruments for each period unless collapsed)
    L(1/.).(l1_dlcapx dls)
Instruments for levels equation
  Standard
    _cons
    l1_xinter4 l1_minter4 y90 y91 y92 y93 y94 y95 y96 y97 y98 y99 y00 y01 y02
    y03 y04 y05 y06 y07
  GMM-type (missing=0, separate instruments for each period unless collapsed)
    D.(l1_dlcapx dls)
------------------------------------------------------------------------------
Arellano-Bond test for AR(1) in first differences: z =  -6.72  Pr > z =  0.000
Arellano-Bond test for AR(2) in first differences: z =  -3.23  Pr > z =  0.001
------------------------------------------------------------------------------
Sargan test of overid. restrictions: chi2(204)  = 621.40  Prob > chi2 =  0.000
  (Not robust, but not weakened by many instruments.)
Hansen test of overid. restrictions: chi2(204)  = 238.63  Prob > chi2 =  0.049
  (Robust, but can be weakened by many instruments.)
Difference-in-Hansen tests of exogeneity of instrument subsets:
  GMM instruments for levels
    Hansen test excluding group:     chi2(184)  = 216.29  Prob > chi2 =  0.052
    Difference (null H = exogenous): chi2(20)   =  22.35  Prob > chi2 =  0.322
  iv(l1_xinter4 l1_minter4 y90 y91 y92 y93 y94 y95 y96 y97 y98 y99 y00 y01 y02 y03 y04 y05 y06 y07, eq(level))
    Hansen test excluding group:     chi2(193)  = 227.63  Prob > chi2 =  0.045
    Difference (null H = exogenous): chi2(11)   =  11.00  Prob > chi2 =  0.443

 
I really appreciate your cooperation!!
 
Caleb


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