The gender pay gap is often justified by the argument that women go into lower-status, less competitive fields. But research has shown that when women saturate a well-compensated field the pay declines, and vice versa. The wages of ticket agents, for example, dropped forty-three per cent between 1950 and 2000, as the job feminized. Computer programmers, meanwhile, made modest wages until men took over much of the profession. Even when you adjust for factors such as education and industry, an unexplained discrepancy of an estimated five per cent persists. In other words, the gender pay gap cannot be explained away by women’s perceived or real choices.