I'm asking because the author talks about the "difference in differences" and as early as highschool physics they drill into your head that the difference betwe

I'm asking because the author talks about the "difference in differences" and as early as highschool physics they drill into your head that the difference between two things is represented by the percentage difference not it's absolute difference. Saying 15% is negligible when it is actually a 100% change in the effect seems incorrect somehow.