My gravity model is to estimate the effect of farm subsidy on farm export. Country fixed effect and time fixed effect exists in my model (The Gravity Equations: Workhorse, Toolkit, and Cookbook mention). My model is attached.
  1. I want to control these fixed effects by adding dummy variables in my model, but it is hard to know when the country fixed effect equal to 0 or 1 in stata.
  2. Ajt includes all the time-varying variables of importer j in year t to reduce the effect of importer country's subsidy on exporter's export. It seems like weird when Ajt combines the country fixed effect and time fixed effect; Bi represent the country fixed effect. Should I change my dummy variables?
  3. Could I use HAUSMAN test to whether fixed effect exists as my solution?
Could you please give me some advice? Thank you so much!

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