PPML fixed effect

[KIM SUJIN]

Dear statalist,

Hello, Im master student who is writing thesis with Gravity PPML model


Dependent variable : Trade Value
Independent variables : Trade Ban

I hope to run regress panel data using PPML method with
country- pair , import_year , export_year dummy variables( fixed effect)


I have 7year, about 170 import, 170 export countries


I tried this stata command~

I tried
ppml_panel_sg Value Ban, export(j) import(i) year(year)

But I got result

'Ban appears to be collinear with your set of fixed effects'


I hope to know how to fix it!!

Thank you all

[Joao Santos Silva]

You did not say how trade ban is defined, but if it does not vary by pair it will be collienar with the fixed effects.

Best wishes,

Joao