[Joao Santos Silva]

Nikos,

Richard already explained (very clearly) the scaling and centering bit. About the choice of estimators, -poisson-, -ppml- and -xtpoisson- all give the same results and you should report those results because they are a well-understood benchmark. You can also report the results obtained with -nbreg- but you need to be careful with the -xtnbreg-. If you want to report the results of -xtnbreg- you need to make sure you understand what you are doing because that is an estimator for a different model.

All the best,

Joao

[Nikos Tsileponis]

Dear Richard, Joao and Carlo,

Thank you so much for your help. You cannot imagine how much I appreciate your help.

It's an honour to take advice from people like you :-)

Best,
Nikos