Dear all,

I need some help to better understand the use of the fixed effects (fe) with xtpoisson.

I am investigating the effect of non-tariff measures (NTMs) on international trade.

I have built a panel database composed of trade volumes for seven years (2012-2018), 50 importers, 150 exporters, and 50 products.
My panel database is constructed:
egen id = group(exporter importer product)
xtset id year

To capture these effects I am using the within estimator following STATA command:

xtpoisson import ntm, fe vce(robust)

I want to test different variations of fixed effects, thus my question is: which of the following fixed effects does the “fe” option include:
  1. Exporter x importer x product
  2. Exporter x year
  3. Exporter
  4. Year
  5. Product x importer
  6. Product
  7. Importer
  8. Product x year
  9. Importer x year
  10. Exporter x product x year
  11. Exporter x importer x year
I would really appreciate your help so as to better understand how to run the model with different fixed effect specification: For example using 1 and 4 in one model, than testing it with 2 and 5 in another model as per points above.


Thank you very much for your help,
G.M.