The point is that the mechanism behind the underrepresentation and behind the 2:1 hiring advantage is the same. Consider: The groups compared in that study are

The point is that the mechanism behind the underrepresentation and behind the 2:1 hiring advantage is the same. Consider: The groups compared in that study are the same size, but we also agree women are underrepresented in the overall group, due to facts that likely cause less-qualified women to leave the group. What do you think happens if you then pick an equal number of men and women from both groups and compare them? Which group will have more qualified candidates? Obviously the women.