“So why would men and women and blacks and whites differ from each other in their occupational choice? We have a few types of wedges. One is discrimination in the labor market. Women and blacks were discriminated against being, say, doctors in 1960, and that discrimination has changed over time. Partners in a medical practice, as well as their customers, are now less likely to see women and blacks as being unable to provide identical services as men and whites. Second are barriers to human capital accumulation among women and blacks. Those explicit and implicit barriers are things like segregation or underinvestment in schools in black neighborhoods, prohibitions on entry of women to certain professional schools, or social norms that steer women toward some occupations and away from others. Third are preferences. Perhaps women and blacks opted out of going into certain professions because of social norms, and they were willing to take a utility loss to not run up against those norms. Fourth are factors that affect home production and have increased labor market flexibility for women over time. This would include labor-saving devices such as dishwashers and washing machines as well as improved methods of birth control that permit greater control over fertility decisions.”