Is the result of the did benchmark regression an average treatment effect

The parallel trend test is testing whether there is a difference in the pre-policy time trend between the treatment and control groups DID allows for a difference between the treatment and control groups.

Multiple-period DID tests the parallel trend hypothesis on the same lines as single-period DID, or through the event study method of decomposition and analysis of the dynamic trend of the economic effects of the policy between years, only in the calculation of the number of policy time points before and after the period is different, the single-period DID is the current time minus the time of policy implementation uniformly, and multiple-period DID is the current time minus the time of implementation of the respective policy .