Occupations are segregated by sex today, but were far more segregated in the early to mid-twentieth century. It is difficult to rationalize sex segregation and “wage discrimination” on the basis of men’s taste for distance from women in the same way differences between other groups in work and housing have been explained. Rather, this paper constructs a “pollution” theory model of discrimination in which occupations are defined by the level of a single-dimensional productivity characteristic. Because there is asymmetric information regarding the value of the characteristic of an individual woman, a new female hire may reduce the prestige of a previously all-male occupation. The predictions of the model include that occupations requiring a level of the characteristic above the female median will be segregated by sex and those below the median will be integrated. The historical record reveals numerous cases of the model’s predictions. For example in 1940 the greater is the productivity characteristic of an office and clerical occupation, the higher the occupational segregation by sex. “Credentialization” that spreads information about individual women’s productivities and shatters old stereotypes can help expunge “pollution.”

Pharmacy has become a female-majority profession that is highly remunerated with a small gender earnings gap and low earnings dispersion relative to other occupations. We sketch a labor market framework based on the theory of equalizing differences to integrate and interpret our empirical findings on earnings, hours of work, and the part-time work wage penalty for pharmacists. Using extensive surveys of pharmacists for 2000, 2004, and 2009 as well as samples from the American Community Surveys and the Current Population Surveys, we explore the gender earnings gap, the penalty to part-time work, labor force persistence, and the demographics of pharmacists relative to other college graduates. We address why the substantial entrance of women into the profession was associated with an increase in their earnings relative to male pharmacists. We conclude that the changing nature of pharmacy employment with the growth of large national pharmacy chains and hospitals and the related decline of independent pharmacies played key roles in the creation of a more family-friendly, female-friendly pharmacy profession. The position of pharmacist is probably the most egalitarian of all U.S. professions today.