Hello all.
For my master thesis I am trying analyse what are the determinants of Non Performing Loans on a sample of banks taken from the Bankscope database.
I have decide to to use both difference GMM and system GMM with the xtabond2. I still have try to use the command since I am making some preliminary consideration and then decide how tu run the model.

My dependent variable is the percentage of NPLs at individual bank's level. As regressor I have the lagged dependent variables plus other individual bank variable and some macroeconomic variables for each country, that are equal for all bank's in a given country (such as the GDP growth)

As I have read from Roodman's paper, one of the key assumption of both estimators is that the errors are not correlated among individuals in the panel. However, given that we are talking about banks, "individuals" that by their very nature are widely interconnected, I think that this assumption is not reliable.

Given the variables included into the regression, I am thinkg about a two-way clustering, at individual level (bank_id) and country level (ISO). When I will run this regression, I will only consider country for which I have AT LEAST 5 banks.

1)Is the two-clustering a correct way to proceed?
2) How can I implement two-way clustering in the xtabond2 syntax? (I am using Stata 14)