I am wondering if there is any reference paper or any explanation guiding how to perform the pre-trend analysis (equation) for this case. I did some searches and saw this topic. However, the answer from the expert not mention the econometrics way or the equation to test pre-trend analysis.
In Dasgupta,2019, last paragraph, section 4.2, I saw a paragraph denoting how he conduct the pre-trend test
To explore the dynamics of the issuance activities and leverage change, we create dummy variables corresponding to the following windows around the treatment year: from 1 to 4 years before the treatment; the treatment year and the 2 years after treatment; the next 3 years; and the years beyond. We find that firms first start growing and issuing equity over the first two sub-periods after the discussion about the leniency law passage started and there is no pre-trend once anticipation effect is taken into account.