Dear all,

I have read various literature which says that time invariant variables tend to be absorbed once the bilateral pair fixed effects are incorporated in the gravity model.

In my case, all the time invariant variables (distance, language, common border and colonizer) have not been absorbed. I can see their coefficients after running the ppml regression (though they are very different from the coefficients when the bilateral pair fixed effects have not been included). Does this mean, there is something which is wrong, or one shouldn't include the time-invariant variables in the model from the onset in the gravity model once the pair-fixed effects have been added?