Earlier quoted context omitted.
So it's making exactly the same mistake as studies that compare the average salary of all working-age women with the average salary of all working-age men, and then declare a "gender pay gap" of 20% (or whatever).
I was thinking the same. The study is stupid, but for the same reason any of the women's pay gap studies in the last few years fall short. Comparing apples and oranges is the new science.
At the end of the day, the problem is that most people (voters) wouldn't even begin to understand or appreciate the distinction between demagoguery and intellectual integrity.