3. There may be crowding of women into certain subfields either because of choice, social norms and mentoring, or entry barriers to other subfields. Because salaries are the result of interactions between supply and demand, increases in supply will put downward pressure on wages in these more female friendly subfields. See Bergman (1974) for a general treatment of this phenomenon.

4. The theory of comparable worth (Bellas 1994) posits that fields that employ a higher proportion of women pay lower salaries because women’s work is devalued by society (Treiman and Hartmann 1991). According to this theory, the suppressing effects of gender composition occurs after controlling for economic factors that affect salaries.

5. Finally, and perhaps most controversially, female scientists and engineers may receive less pay than men for equal work as a result of subtle or blatant discrimination by employers. This discrimination may take the form of lower wages for women doing the same work as men at all levels of experience. For example, Bellas (1994) and Ahern and Scott (1981) found that the effects of experience on salary were larger for men than women, indicating that men are compensated more than women for any given level of experience. Discrimination may also be reflected in society’s tendency to devalue women’s work, paying lower salaries in fields where large numbers of women work (see point 4 above). Or, discrimination may come in the form of barriers to entry into certain prestigious subfields or jobs resulting in crowding of women into less prestigious, lower paying alternatives.

In this chapter we use data from four years of the SDR to examine the extent and causes of gender differences in salaries. We begin by describing the gross gender differences in salaries without controls for characteristics of either individuals or their employers. We find that men have had a nearly constant 20 percent advantage in salary during the 23 years from 1973 to 1995. To understand why men receive higher salaries and why there has not been an improvement, we add controls for variables that have been suggested by prior research. This is done initially by simply comparing the median salaries of men and women in, for example, the same fields or with the same year of Ph.D. To control simultaneously for a large number of factors, we estimate a series of multiple regressions. The differing characteristics of men and women, such as in experience and field of study, can explain much of the gross gender difference in salary. However, even with numerous controls, gender differences in salary remain. Reasons for these differences are discussed in the summary.