. xtabond2 F2.bpip bpip md bmifat2 bmithin dent sis bro age csch inc ,gmm(F2.b pip, lag(2 2)) iv(md bmifat2 bmithin dent sis bro age csch inc) twostep
Favoring space over speed. To switch, type or click on mata: mata set matafavor speed, perm.
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: cpubid                          Number of obs      =     14348
Time variable : year                            Number of groups   =      5551
Number of instruments = 58                      Obs per group: min =         1
Wald chi2(10) =  96835.93                                      avg =      2.58
Prob > chi2   =     0.000                                      max =         5

F2.bpip       Coef.   Std. Err.      z    P>z     [95% Conf. Interval]

bpip    .9622903   .0186582    51.57   0.000     .9257209    .9988598
md    .0835154   .1194214     0.70   0.484    -.1505463    .3175771
bmifat2     .280327   .5435837     0.52   0.606    -.7850776    1.345732
bmithin     -.60356   .6250027    -0.97   0.334    -1.828543    .6214229
dent    .1130063   .4005308     0.28   0.778    -.6720198    .8980323
sis   -.0818067   .1707541    -0.48   0.632    -.4164785    .2528652
bro   -.2320763   .1719287    -1.35   0.177    -.5690504    .1048977
age    .2016487   .0699208     2.88   0.004     .0646065    .3386909
csch   -.7266028   .6754149    -1.08   0.282    -2.050392     .597186
inc   -.0042888   .0048576    -0.88   0.377    -.0138095    .0052319
_cons           0  (omitted)

Warning: Uncorrected two-step standard errors are unreliable.

Instruments for first differences equation
Standard
D.(md bmifat2 bmithin dent sis bro age csch inc)
GMM-type (missing=0, separate instruments for each period unless collapsed)
L2.F2.bpip
Instruments for levels equation
Standard
md bmifat2 bmithin dent sis bro age csch inc
_cons
GMM-type (missing=0, separate instruments for each period unless collapsed)
DL.F2.bpip

Arellano-Bond test for AR(1) in first differences: z =      .  Pr > z =      .
Arellano-Bond test for AR(2) in first differences: z =      .  Pr > z =      .

Sargan test of overid. restrictions: chi2(47)   =   0.00  Prob > chi2 =  1.000
(Not robust, but not weakened by many instruments.)
Hansen test of overid. restrictions: chi2(47)   =   0.00  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(22)   =   0.00  Prob > chi2 =  1.000
Difference (null H = exogenous): chi2(25)   =  -0.00  Prob > chi2 =  1.000
iv(md bmifat2 bmithin dent sis bro age csch inc)
Hansen test excluding group:     chi2(38)   =   0.00  Prob > chi2 =  1.000
Difference (null H = exogenous): chi2(9)    =   0.00  Prob > chi2 =  1.000


p值都是1，AR检验的p值为1，不知道哪里错了，求高人指点！
感谢！