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Assuming that the coefficients are at a comparable scale, you could probably use the suest command to combine the two regressions. Then you can test for equality of the coefficients with the test command. For this to work, you need to run the two xtdpdgmm regressions with the auxiliary option, store the results with estimates store, and then call suest with the two stored estimation results.
I have two equations of dynamic panel data. One is y=b0+b1x1+b2x2+b3x3, and the other is y=A0+A1x1+A2x4+A3x5. I get the coefficients through the xtdpdgmm. Now, I want to compare b2 and A3 to know which has a larger effect on y. Would you give me some advice?
xtdpdgmm does not provide standardized regression coefficients. You would need to standardize all of your variables manually before running the regression.
I can hardly imagine a situation in the context of dynamic panel models where this is meaningful. There is a lot of things that can go wrong and the interpretation of the results becomes anything than straightforward.
Hello Dr. Kripfganz, how can i get standard regression coefficents from your xtdpdgmm? As far as I know,your xtdpdgmm presents nonstandard coefficents.
The GMM estimators implemented in xtdpdgmm (or xtabond2) are intended for setting with large N relative to T. Your data set does not really fit into that category. It neither fits into the large-N, large-T world. With small N, you cannot expect to reliably estimate the optimal weighting matrix. Thus, any two-step GMM estimator (that allows for arbitrary correlation within groups over time) is eliminated from the discussion. Similarly, it is not recommended to compute robust standard errors clustered at the group level. You could still use a conventional IV/2SLS estimator with ivregress or xtivreg.
Hello Dr. Kripfganz,
I really appreciate all your work.
I am currently having trouble with my dynamic model. N = 15. T = 64.
The empiric evidence in my paper offers a variety of dynamic panels being made and because there is endogeneity I decided to give it a try to your work in order to achieve the best results.
in xtabond2 I had the best model by making all my variables strictly exogenous and only having the lagged depedent variable in the gmm side. But that is not what I intended.
For long panels, which dynamic panel model could I use as an alternative? Or should I just stay with a xtreg fe despite endogeneity being present?
I find that your margins and marginsplot can only analyze the interaction of one categorical variable and continuous variable or two categorical variables. But I want to analyze the interaction of two continuous variables, how can I do?
I am sorry that the bug had significant effects on your results.
From your results, it seems that there are some issues primarily related to the variables offideputy and offdepdyn. But there is not much more I can say about that. While this is probably not satisfying, sometimes we may just have to live with some imperfection in our models. If you can justify your model specification on theoretical grounds, it might be acceptable to put less emphasis on the specification tests. This also depends on whether the troublesome variables are your main variables of interest or just some control variables. The specification tests then could tell us that we need to be cautious with the interpretation of our results. A perfect model may not exist given the available data.
Arellano-Bond test for autocorrelation of the first-differenced residuals
H0: no autocorrelation of order 1: z = -2.6878 Prob > |z| = 0.0072
H0: no autocorrelation of order 2: z = -0.7629 Prob > |z| = 0.4455
H0: no autocorrelation of order 3: z = 0.7649 Prob > |z| = 0.4444
.
. estat overid
Sargan-Hansen test of the overidentifying restrictions
H0: overidentifying restrictions are valid
collinearity check...
collinearities detected in [Y X] (right to left): 0o.offideputy#co.dynamics
collinearities detected in [Y X Z] (right to left): __alliv_51 __alliv_50 __alliv_49 __alliv_48 __alliv_47 __alliv_46 __alliv_45 __alliv_40
> __alliv_39 __alliv_37 __alliv_33 0o.offideputy#co.dynamics
collinearities detected in [X Z Y] (right to left): 2011.year 2010.year 2009.year 2008.year 2007.year 2006.year 2005bn.year 0o.offideputy#co
> .dynamics agee sex edu area
warning: collinearities detected, reparameterization may be advisable
Overidentification test: Kleibergen-Paap robust LIML-based (LM version)
Test statistic robust to heteroskedasticity and clustering on code
j= 19.93 Chi-sq( 25) p-value=0.7506
Underidentification test: Kleibergen-Paap robust LIML-based (LM version)
Test statistic robust to heteroskedasticity and clustering on code
j= 20.84 Chi-sq( 26) p-value=0.7501
From a programmer's perspective, factor variables and interaction terms are some of the nastiest animals in the Stata universe. They always find a way to escape your carefully designed algorithms. So it happened again with xtdpdgmm. There was unfortunately an annoying bug that could result in incorrect estimates when interaction terms were specified as instruments. I hopefully now managed to tame these animals once and for all with the latest bug fix.
Version 2.3.1 is now available on my personal website and on SSC (with the usual thanks to Kit Baum).
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