After all the adjustments, the remaining 8-percentage-point unexplained gender gap could reflect discrimination, write Blau and Kahn, pointing to academic studies. In one, when five symphony orchestras shifted to blind auditions, with candidates’ identities unknown, women’s success rates shot up. In another study, men and women with similar résumés applied for waitstaff jobs at high-priced restaurants; women’s job offers were 50 percent lower than men’s.

But the persisting gap could have other causes. There’s “the motherhood wage penalty”: Women bear the greatest responsibilities for child-rearing. Careers are interrupted; even when employers allow greater job flexibility, incomes and advancement prospects suffer.

Men can continue climbing career ladders, while many women are stalled or stopped. That’s one reason wage gaps between men and women are greatest among the best-paid workers, say Blau and Kahn. It also helps explain why there are so few female chief executives: about 4 percent of Fortune 500 firms employ them. On the other hand, the pleasures and duties of being a parent often dwarf on-the-job rewards. Either way, hard economic and emotional choices often can’t be avoided.