大家帮看看 命令写对了嘛？还有要显著应该如何改进
xtabond2 y L.y w1 w2 w3 w4 x  , gmm(L.y , lag(2 2)) robust twostep
Favoring space over speed. To switch, type or click on mata: mata set matafavor speed, perm.
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
------------------------------------------------------------------------------
Group variable: ind                             Number of obs      =        25
Time variable : ye                              Number of groups   =         5
Number of instruments = 8                       Obs per group: min =         5
Wald chi2(6)  =  34875.94                                      avg =      5.00
Prob > chi2   =     0.000                                      max =         5
------------------------------------------------------------------------------
             |              Corrected
           y |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
           y |
         L1. |   1.263574   .2739936     4.61   0.000     .7265561    1.800591
             |
          w1 |   .0273071   .0882445     0.31   0.757    -.1456488    .2002631
          w2 |  -.2577186   .2987039    -0.86   0.388    -.8431674    .3277303
          w3 |  -.3964281   .6680444    -0.59   0.553    -1.705771     .912915
          w4 |   .3347015   .5379795     0.62   0.534    -.7197189    1.389122
           x |          0  (omitted)
       _cons |          0  (omitted)
------------------------------------------------------------------------------
Instruments for first differences equation
  GMM-type (missing=0, separate instruments for each period unless collapsed)
    L2.L.y
Instruments for levels equation
  Standard
    _cons
  GMM-type (missing=0, separate instruments for each period unless collapsed)
    DL.L.y
------------------------------------------------------------------------------
Arellano-Bond test for AR(1) in first differences: z =   0.06  Pr > z =  0.951
Arellano-Bond test for AR(2) in first differences: z =   1.09  Pr > z =  0.276
------------------------------------------------------------------------------
Sargan test of overid. restrictions: chi2(1)    =   0.56  Prob > chi2 =  0.454
  (Not robust, but not weakened by many instruments.)
Hansen test of overid. restrictions: chi2(1)    =   0.00  Prob > chi2 =  1.000
  (Robust, but weakened by many instruments.)

.