st: GMM diff vs sys and convergence rate

[<irodriguez@utdt.edu>]

Dears,

I have a panel dataset for a sample of 20 countries over 8 periods I`ve
use GMM method to estimate a model of convergence like this
yit=b yit-1 + q xit + uit
where xit are exogenous variables

-I could be posible that difference GMM work better than sysyem GMM?
-How can I calculate the convergence rate?

Thank you a lot

Ines



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