Hi,

I am running a trade gravity model.

When I run the model with OLS, the number of observations is the same even if I run the model without or with exporter-time and importer-time fixed effects.

However, when I run the model with PPMLHDFE the number of observations is higher when I run the model without the fixed effects than when I run the model with the fixed effects.

Which do you think could be the reason?

Thanks!