The assertion holds true! It's just the xtabond2 always reports two-step Sargan test even after a one-step estimation and vice versa.
In terms of Difference-in-Sargan coding I'd like to point out, that in the coming 'name space of non-standard models' an accessor for the number of instruments should be present too. Thanks for the many comments and advice! Cheers Leon 01.07.2013 04:10, Allin Cottrell: > On Sun, 30 Jun 2013, Pindar wrote: > >> I'm still struggling with the dpanel methodology and the comparison of >> results to e.g. Stata. >> First, the Sargan test statistics reported by GRETL are equivalent to the >> ones of Arellano and Bond (1991) Sargan tests. > Yes; and in most cases they are identical with those produced by > Ox/DPD. In gretl we use the formula given in the DPD manual to > compute the Sargan test -- maybe this should be given in the User's > Guide. > >> The assertion that the Sargan test of GRETL is the Hansen test in xtabond >> seems not to be true for *xtabond2*. > In some cases the assertion holds true, maybe not in others. > >> GRETL values are always closer to the Sargan tests of Roodman reported in >> Roodman (2006). What is the Hansen test then? > Ask Roodman, or another Stata guru. I don't know. It's not > adequately documented in the xtabond2 PDF file. > >> In Baltagi (2005) I found a xtabond output. Here the results for GMM-Diff >> one-step estimates are the same as of gretl and the Sargan test fits too >> (note, here is only a Sargan test is reported in the output). >> Strange in this comparison: In GRETL the two-step estimators are far away >> from the one-step coefficients and completely different to the ones reported >> in Baltagi (p. 157). > This is a case where the "A" matrix is singular and so -- as > explained in the Gretl User's Guide -- all bets are off. Gretl and > Ox/DPD do the same thing (generalized inverse, Moore-Penrose). Stata > apparently does something else, we don't know what. > >> Another questions is how to perform the >> Difference-in-Sargan/Hansen tests in GRETL (as reported in >> xtabond2)? > At this point you'd have to code that yourself. > > Allin Cottrell > _______________________________________________ > Gretl-users mailing list > Gretl-users(a)lists.wfu.edu > http://lists.wfu.edu/mailman/listinfo/gretl-users
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The assertion holds true!
It's just the xtabond2 always reports two-step Sargan test even after a one-step estimation and vice versa. In terms of Difference-in-Sargan coding I'd like to point out, that in the coming 'name space of non-standard models' an accessor for the number of instruments should be present too. Thanks for the many comments and advice! Cheers Leon 01.07.2013 04:10, Allin Cottrell: On Sun, 30 Jun 2013, Pindar wrote:I'm still struggling with the dpanel methodology and the comparison of results to e.g. Stata. First, the Sargan test statistics reported by GRETL are equivalent to the ones of Arellano and Bond (1991) Sargan tests.Yes; and in most cases they are identical with those produced by Ox/DPD. In gretl we use the formula given in the DPD manual to compute the Sargan test -- maybe this should be given in the User's Guide.The assertion that the Sargan test of GRETL is the Hansen test in xtabond seems not to be true for *xtabond2*.In some cases the assertion holds true, maybe not in others.GRETL values are always closer to the Sargan tests of Roodman reported in Roodman (2006). What is the Hansen test then?Ask Roodman, or another Stata guru. I don't know. It's not adequately documented in the xtabond2 PDF file.In Baltagi (2005) I found a xtabond output. Here the results for GMM-Diff one-step estimates are the same as of gretl and the Sargan test fits too (note, here is only a Sargan test is reported in the output). Strange in this comparison: In GRETL the two-step estimators are far away from the one-step coefficients and completely different to the ones reported in Baltagi (p. 157).This is a case where the "A" matrix is singular and so -- as explained in the Gretl User's Guide -- all bets are off. Gretl and Ox/DPD do the same thing (generalized inverse, Moore-Penrose). Stata apparently does something else, we don't know what.Another questions is how to perform the Difference-in-Sargan/Hansen tests in GRETL (as reported in xtabond2)?At this point you'd have to code that yourself. Allin Cottrell _______________________________________________ Gretl-users mailing list [email protected] http://lists.wfu.edu/mailman/listinfo/gretl-users |
