single academic institution (see, for example, Becker and Toutkoushian 1995; Ferber 1974; Fox 1981; Gordon, Morton, and Braden 1974; Hoffman 1976; Katz 1973). Single institution studies have the advantage of more detailed data on each individual and are based on a more complete understanding of the nuances of the local context of employment, but they are limited by the unique characteristics of that institution. A second type of study uses a large sample to study differences across fields, and often across sectors of employment. For example, Ferber and Kordick (1978) examined Ph.D.s in all fields with degrees from 1958–63 and 1967–72. Ahern and Scott (1981), the precursor to our study, examined salaries in five broad fields for Ph.D.s from the 1940s through the early 1970s. Many of these studies of salary are restricted to academics, such as Barbezat (1988), Farber (1977), Gregorio, Lewis, and Wanner (1982), Johnson and Stafford (1979), and Tolbert (1986), or a single field such as Hansen, Weisbrod, and Strauss (1978) or Morgan (1998).
While studies of salary differences for men and women in science and engineering differ widely in their samples, focus, and methodology, each study has found that the average female scientist or engineer earns less than her male counterpart. There have been several proposed explanations for this gap in earnings:
Women earn less because they are less qualified than men. While our analysis in earlier chapters found few gender differences in educational backgrounds, it is still possible that qualifications attained at the completion of formal education may be lower. Due to longer periods out of the labor force, women accumulate fewer years of experience and during periods of absence from S&E their skills may depreciate. Consequently, when women reenter the S&E labor force they will earn a lower salary than at the time of exit and will have foregone the salary increases due to accumulated experience. In anticipation of time out of the labor market, women may choose to invest less in on the job training or employers may invest less in female employees. Lower investment in training early in the career will produce lower future female earnings (Duncan and Hoffman 1979). Or, even with similar education and experience, women may be less productive than men in the scientific workplace. See Cole and Zuckerman (1984), Long (1992), and Xie and Shauman (1998) for a review of the literature on gender differences in productivity.
Cumulative advantage, as defined by Merton (1973 reprinted from 1942), suggests that men are the beneficiaries of gender inequities early in the career and that these early advantages are magnified over time. Even if salary is based entirely on productivity, early disadvantages in employment for women may lead to a pay gap that will grow over the course of their careers.