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st: FW: Use of xtabond2


From   "Mavilde Modesto" <mavildemodesto@netcabo.pt>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: FW: Use of xtabond2
Date   Mon, 10 Jun 2013 22:47:55 +0100

Dear Statalist,

I am a new user of Stata and I do not Know enough to solve those Two
"Warnings" I have got  running xtabond2. 

The first one I do not understand because I use 49 instruments but I have
got 510 observations.

About the second warning anyone can help me indicating which command should
I use to produce and use the generalized inverse to calculate optimal
weighting matrix for two-step estimation and how to proceed?

I would be so grateful!

Here are the results I have got:

xi: xtabond2 logGVApc l.logGVApc logPubInvpc logProductiv
i.yearid,gmm(logGVApc,lag(2 2)) iv(i.yearid) robust twostep small/*2
lag*//*considering Public Investment as exogenous*/ i.yearid _Iyearid_1-18
(naturally coded; _Iyearid_1 omitted) Favoring speed over space. To switch,
type or click on mata: mata set matafavor space, perm.
_Iyearid_18 dropped due to collinearity

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: id Number
of obs = 510 Time variable : Periodo Number of groups = 30 Number of
instruments = 49 Obs per group: min = 17 avg = 17.00 F(19, 29) = 967.14 Prob
> F = 0.000 max = 17

logGVApc Coef. Corrected Std. Err. t P>t [95% Conf. Interval]

logGVApc
L1. .682456 .1063249 6.42 0.000 .4649971 .8999149

logPubInvpc -.0131582 .033408 -0.39 0.697 -.0814852 .0551688 logProductiv
.3087351 .1130752 2.73 0.011 .0774704 .5399997
_Iyearid_2 -.0068182 .0563709 -0.12 0.905 -.1221097 .1084733
_Iyearid_3 .0011161 .0454337 0.02 0.981 -.0918064 .0940385
_Iyearid_4 -.0114692 .0372671 -0.31 0.760 -.0876889 .0647506
_Iyearid_5 .0045814 .0361524 0.13 0.900 -.0693586 .0785214
_Iyearid_6 -.0350082 .03002 -1.17 0.253 -.096406 .0263896
_Iyearid_7 -.0075198 .0267703 -0.28 0.781 -.0622712 .0472316
_Iyearid_8 -.0195811 .028722 -0.68 0.501 -.0783242 .039162
_Iyearid_9 .0031761 .020015 0.16 0.875 -.0377591 .0441114 _Iyearid_10
.0003316 .0215934 0.02 0.988 -.0438319 .044495
_Iyearid_11 .0088895 .0172075 0.52 0.609 -.0263038 .0440827
_Iyearid_12 .0194218 .0134674 1.44 0.160 -.0081222 .0469658
_Iyearid_13 .0252198 .0125812 2.00 0.054 -.0005116 .0509512
_Iyearid_14 .0273918 .0257642 1.06 0.296 -.0253019 .0800856
_Iyearid_15 .011291 .0230309 0.49 0.628 -.0358124 .0583944
_Iyearid_16 .0043055 .0191247 0.23 0.823 -.0348089 .0434199
_Iyearid_17 .0141141 .0165234 0.85 0.400 -.0196801 .0479083 _cons -.2379976
.3225759 -0.74 0.467 -.8977395 .4217443 Instruments for first differences
equation Standard
D.(_Iyearid_2 _Iyearid_3 _Iyearid_4 _Iyearid_5 _Iyearid_6 _Iyearid_7
_Iyearid_8 _Iyearid_9 _Iyearid_10 _Iyearid_11 _Iyearid_12 _Iyearid_13
_Iyearid_14 _Iyearid_15 _Iyearid_16 _Iyearid_17 _Iyearid_18) GMM-type
(missing=0, separate instruments for each period unless collapsed)
L2.logGVApc Instruments for levels equation Standard
_Iyearid_2 _Iyearid_3 _Iyearid_4 _Iyearid_5 _Iyearid_6 _Iyearid_7
_Iyearid_8 _Iyearid_9 _Iyearid_10 _Iyearid_11 _Iyearid_12 _Iyearid_13
_Iyearid_14 _Iyearid_15 _Iyearid_16 _Iyearid_17 _Iyearid_18 _cons GMM-type
(missing=0, separate instruments for each period unless collapsed)
DL.logGVApc

Arellano-Bond test for AR(1) in first differences: z = -2.60 Pr > z = 0.009
Arellano-Bond test for AR(2) in first differences: z = 1.33 Pr > z = 0.185

Sargan test of overid. restrictions: chi2(29) = 68.55 Prob > chi2 = 0.000
(Not robust, but not weakened by many instruments.)

Hansen test of overid. restrictions: chi2(29) = 17.64 Prob > chi2 = 0.951
(Robust, but weakened by many instruments.) Difference-in-Hansen tests of
exogeneity of instrument subsets:
GMM instruments for levels

Hansen test excluding group: chi2(13) = 17.64 Prob > chi2 = 0.172 Difference
(null H = exogenous): chi2(16) = 0.00 Prob > chi2 = 1.000
iv(_Iyearid_2 _Iyearid_3 _Iyearid_4 _Iyearid_5 _Iyearid_6 _Iyearid_7
_Iyearid_8 _Iyearid_9 _Iyearid_10 _Iyearid_11 _Iyearid_12 _Iyearid_13
_Iyearid_14 _Iyearid_15 _Iyearid_16 _Iyearid_17 _Iyearid_18) Hansen test
excluding group: chi2(13) = 10.44 Prob > chi2 = 0.657 Difference (null H =
exogenous): chi2(16) = 7.20 Prob > chi2 = 0.969

Mavilde Modesto
Universidade Católica Portuguesa



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