When Billie Jean King won the United States Open singles tennis title in 1972, her reward was a meager $10,000. Ilie Năstase, her male counterpart, won $25,000.

Ms. King fought hard for equal rights and, on the tennis court, she won. By 1973, men and women received the same prizes at the Open. That still can’t be said of all tennis tournaments, but despite some ill-natured male grousing recently, equal pay is still the rule at the United States Open, at least.

That is not the reality in the overall labor market, however, where women still earn less than men and there is considerable confusion about the reasons for the gender earnings gap — and about what can be done to eliminate it.

Fighting to eradicate discriminatory employment practices is absolutely needed, of course. I’ve spent many years studying this subject, and my research shows that unequal treatment in hiring and in the work setting is real and may be reflected in unequal pay.