Dear sir/madam,

I found a paper where the authors use a difference-in-difference approach and as a robustness check they interact all their control variables with their #post dummy. Could anyone explain if this is a common robustness check for difference-in-difference and what the rationale behind it is (instead of just adding the controls without interaction)?

I am referring to the following paper: Title: "When investors call for climate responsibility, how do mutual funds respond?", Authors: Ceccarelli , Ramelli & Wagner (2019), page 50.

Thank you very much in advance.

Kind regards,
Rudolf