Dear all.
I need your help.
I am working in a gravity model that pretends to estimate Colombian exports to 136 partners from 2005 to 2018 through the PPML approach.
Therefore, the dataset includes only exports from Colombia to its partners (one exporter; 136 importers).
My questions are:
1. Is it necessary to include time fixed effects?
2. Is it compulsory to estimate the specification with cluster by country or distance? Or is it right to estimate it with robust standard error as usually?
Thanks in advance.
Regards.