第一次用系统GMM方法，按部就班地按照网上的资料修改了程序，不知道跑出来的这个结果能不能用，希望大家帮忙分析指正一下哇！
475个公司的10年数据，程序是：xtabond2 lnl l.lnl lny lnk, gmm(l.lnl) iv(lny lnk) nolevel twostep robust

Dynamic panel-data estimation, two-step difference GMM
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Group variable: stkcd                           Number of obs      =      3778
Time variable : accper                          Number of groups   =       475
Number of instruments = 38                      Obs per group: min =         2
Wald chi2(3)  =    473.92                                      avg =      7.95
Prob > chi2   =     0.000                                      max =         8
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             |              Corrected
         lnl |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
         lnl |
         L1. |   .4895885   .0749475     6.53   0.000     .3426941    .6364829
             |
         lny |   .2367237   .0429589     5.51   0.000     .1525259    .3209215
         lnk |   .0941103   .0329993     2.85   0.004     .0294329    .1587877
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Instruments for first differences equation
  Standard
    D.(lny lnk)
  GMM-type (missing=0, separate instruments for each period unless collapsed)
    L(1/9).L.lnl
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Arellano-Bond test for AR(1) in first differences: z =  -6.11  Pr > z =  0.000
Arellano-Bond test for AR(2) in first differences: z =  -0.32  Pr > z =  0.751
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Sargan test of overid. restrictions: chi2(35)   =  80.56  Prob > chi2 =  0.000
  (Not robust, but not weakened by many instruments.)
Hansen test of overid. restrictions: chi2(35)   =  40.18  Prob > chi2 =  0.251
  (Robust, but can be weakened by many instruments.)

Difference-in-Hansen tests of exogeneity of instrument subsets:
  
    Hansen test excluding group:     chi2(33)   =  38.66  Prob > chi2 =  0.229
    Difference (null H = exogenous): chi2(2)    =   1.52  Prob > chi2 =  0.468

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