[Joao Santos Silva]

Dear Noemi Seng,

The variables that are dropped by ppmlhdfe should be dropped; the estimates of the coefficients you get for them with ppml are meaningless.

Best wishes,

Joao

[Joao Santos Silva]

Dear Noemi Seng,

The variables dropped by ppmlhdfe should be dropped because their effects are not identified. The coefficient estimates you get for those variables with ppml are meaningless; ppml will also drop these variables if you write the command including all fixed effects immediately after the dependent variable.

Best wishes,

Joao