Perfect Doctor Violates Parallel Trends: Step 4(e) in Pedro's DiD Checklist

We’ve been in step 4 of Pedro’s difference-in-differences checklist for around two weeks. The step reads:

Step 4: Choose the comparison groups and the parallel trend assumption carefully: Who decides treatment? What do they know? What type of selection is allowed?

I’ve previously written four entries about this step. They were:

1. Step 4a: Selection into t…