- Any attributes not accounted for in part or in full. (Of which there are quite a lot.)

- Past sexism which impacts income in the modern day. (Sexism 30 years ago would have impacted starting incomes of people, which would have reflected up til today because one's initial compensation greatly impacts future compensation through many different factors.)

- Modern day sexism.

Given evidence such as looking at just the youngest generation and what they earn, you begin to see women not only equalizing with men in earnings, but out pacing them. This means that 5 to 7% gap is far more likely to be the first and second. And once you compare pay gaps to things like danger of the jobs chosen, you see there are many more factors that are hard to account for because people differ so much in how they view the worthiness of these factors.

Also some things often aren't accounted for. Consider that many studies looking at the pay gap compare full time work to full time work, not differentiating the difference between 37.5 hours a week (full time in government) and 80 hours a week (or even worse at a startup). BUT... even in the studies that do try to compare these, they don't compare the relevant experience gains (the person working 60 hours a week average will gain 1.5 times the experience of someone working 40 hours a week, to say nothing of the potential differences in those who go home and work on related not-work projects).

In short, once you account for all of these and look at those entering the work force, it turns out the pendulum has already swung the other way.

On a side note, there are even reports coming out that this may be impacting the dating market due to social pressures on both men and women to pair up in specific patterns (namely that the man should be making no less than the woman that he is dating and that he should be no less educated than her). While these social pressures are definitely weakening compared to past generations, they are not by any means gone yet.