I am running the following command for my research and I just cannot pass the Hansen Test for Overid, which means to accept the null hypothesis.

Is there anyone who can advise me on this issues?

Any help would be appreciated very much.

Thank you!


The command and the result are as follows:

xtabond2 log_tfp_op l.log_tfp_op fr log_hhi log_tr log_tr2 i.dbj_securitycode_m if regyear >=2000 & dbj_securitycode_l==1 & ri_total_1977_new>0, gmm(l.log_tfp_op fr, lag(2 5))
> iv(log_hhi log_tr log_tr2 ) twostep robust


Favoring speed over space. To switch, type or click on mata: mata set matafavor space, 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: companycode Number of obs = 15713
Time variable : regyear Number of groups = 1394
Number of instruments = 174 Obs per group: min = 1
Wald chi2(20) = 345.03 avg = 11.27
Prob > chi2 = 0.000 max = 17
------------------------------------------------------------------------------------
| Corrected
log_tfp_op | Coef. Std. Err. z P>|z| [95% Conf. Interval]
-------------------+----------------------------------------------------------------
log_tfp_op |
L1. | .3476721 .067836 5.13 0.000 .214716 .4806281
|
fr | .173543 .0292111 5.94 0.000 .1162903 .2307958
log_hhi | -.1147098 .0157331 -7.29 0.000 -.1455461 -.0838734
log_tr | .0885671 .0872536 1.02 0.310 -.0824467 .2595809
log_tr2 | -.0017039 .0017581 -0.97 0.332 -.0051497 .001742
|
dbj_securitycode_m |
1 | 0 (empty)
2 | .1763768 .1745827 1.01 0.312 -.1657991 .5185527
3 | .2285341 .2859776 0.80 0.424 -.3319717 .7890398
4 | -.1442419 .3324066 -0.43 0.664 -.7957468 .5072631
5 | .4348618 .2471303 1.76 0.078 -.0495047 .9192283
6 | -.1818706 .0913705 -1.99 0.047 -.3609534 -.0027877
7 | -.0538582 .3097286 -0.17 0.862 -.6609151 .5531987
8 | -.0887699 .1396929 -0.64 0.525 -.362563 .1850231
9 | .0749684 .0879994 0.85 0.394 -.0975072 .247444
10 | -.0111053 .0990612 -0.11 0.911 -.2052617 .1830511
11 | .1041381 .1332358 0.78 0.434 -.1569992 .3652754
12 | -.041476 .0699862 -0.59 0.553 -.1786465 .0956945
13 | -.1542583 .0732315 -2.11 0.035 -.2977894 -.0107271
14 | -.1235564 .0880978 -1.40 0.161 -.296225 .0491121
15 | .122753 .1945506 0.63 0.528 -.2585591 .5040651
|
_cons | .87274 1.087934 0.80 0.422 -1.259572 3.005052
------------------------------------------------------------------------------------
Instruments for first differences equation
Standard
D.(log_hhi log_tr log_tr2)
GMM-type (missing=0, separate instruments for each period unless collapsed)
L(2/5).(L.log_tfp_op fr)
Instruments for levels equation
Standard
log_hhi log_tr log_tr2
_cons
GMM-type (missing=0, separate instruments for each period unless collapsed)
DL.(L.log_tfp_op fr)
------------------------------------------------------------------------------
Arellano-Bond test for AR(1) in first differences: z = -4.25 Pr > z = 0.000
Arellano-Bond test for AR(2) in first differences: z = -0.27 Pr > z = 0.786
------------------------------------------------------------------------------
Sargan test of overid. restrictions: chi2(153) =1229.64 Prob > chi2 = 0.000
(Not robust, but not weakened by many instruments.)
Hansen test of overid. restrictions: chi2(153) = 415.83 Prob > chi2 = 0.000
(Robust, but weakened by many instruments.)

Difference-in-Hansen tests of exogeneity of instrument subsets:
GMM instruments for levels
Hansen test excluding group: chi2(119) = 311.91 Prob > chi2 = 0.000
Difference (null H = exogenous): chi2(34) = 103.92 Prob > chi2 = 0.000
iv(log_hhi log_tr log_tr2)
Hansen test excluding group: chi2(150) = 387.92 Prob > chi2 = 0.000
Difference (null H = exogenous): chi2(3) = 27.91 Prob > chi2 = 0.000