. xtabond2 lncases lnincome lngdp  lnpcdi law , gmmstyle(lncases lnincome lngdp  lnpcdi law ) two
> step
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Warning: Number of instruments may be large relative to number of observations.
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/Hansen statistics may be negative.

Dynamic panel-data estimation, two-step system GMM
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Group variable: area                            Number of obs      =       310
Time variable : year                            Number of groups   =        31
Number of instruments = 208                     Obs per group: min =        10
Wald chi2(4)  =   6867.13                                      avg =     10.00
Prob > chi2   =     0.000                                      max =        10
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     lncases |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
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    lnincome |   .3715157   .0602629     6.16   0.000     .2534026    .4896287
       lngdp |   .8788493    .048182    18.24   0.000     .7844144    .9732842
      lnpcdi |   .5956925   .0914476     6.51   0.000     .4164585    .7749266
         law |  -.2291436   .0183269   -12.50   0.000    -.2650637   -.1932234
       _cons |  -4.476327   .3986447   -11.23   0.000    -5.257656   -3.694998
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Warning: Uncorrected two-step standard errors are unreliable.

Instruments for first differences equation
  GMM-type (missing=0, separate instruments for each period unless collapsed)
    L(1/9).(lncases lnincome lngdp lnpcdi law)
Instruments for levels equation
  Standard
    _cons
  GMM-type (missing=0, separate instruments for each period unless collapsed)
    D.(lncases lnincome lngdp lnpcdi law)
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Arellano-Bond test for AR(1) in first differences: z =  -0.47  Pr > z =  0.636
Arellano-Bond test for AR(2) in first differences: z =  -3.84  Pr > z =  0.000
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Sargan test of overid. restrictions: chi2(203)  =1727.53  Prob > chi2 =  0.000
  (Not robust, but not weakened by many instruments.)
Hansen test of overid. restrictions: chi2(203)  =  30.24  Prob > chi2 =  1.000
  (Robust, but weakened by many instruments.)

Difference-in-Hansen tests of exogeneity of instrument subsets:
  GMM instruments for levels
    Hansen test excluding group:     chi2(168)  =  30.50  Prob > chi2 =  1.000
    Difference (null H = exogenous): chi2(35)   =  -0.26  Prob > chi2 =  1.000


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