[Clyde Schechter]

The -if e(sample)- part is only valid when used after an estimation command (a regression model). So you have to rerun your regression before you use that. Once the regression is run, -if e(sample)- will remain valid until you either run another estimation command (another regression, or -margins, post-, a few others), or close your Stata session.

[Celine Tran]

Clyde Schechter Thank you very much !