Female early-career scientists have conducted less interdisciplinary research in the past six decades: evidence from doctoral theses

Interdisciplinary research is a driving force of transformative and innovative science, yet it remains unclear how early-career scientists pursue interdisciplinary research paths. Analyzing data from 675,135 doctoral theses of U.S. Ph.D. graduates who graduated from 1950 to 2016, we study the development of interdisciplinary doctoral theses in the five scientific domains of behavioral sciences, biological sciences, engineering, health and medical sciences, and mathematical and physical sciences. We propose an indicator to measure the degree of interdisciplinarity embedded in the doctoral research by employing co-occurrence matrices of subjects assigned to doctoral theses in the ProQuest Dissertations & Theses Database. This study finds that interdisciplinary doctoral theses have exhibited a growing trend across different scientific domains, and universities of varying research intensity. Since the 1990s, interdisciplinary research has played a dominant role in doctoral theses within the five scientific domains. The results of multivariate regression models suggest persistent gender disparities in the interdisciplinarity level of doctoral theses. Specifically, male-authored doctoral theses demonstrate a higher level of interdisciplinarity than female-authored doctoral theses. In addition, this study suggests that being supervised by female advisors may amplify gender disparities in the interdisciplinarity level of their students' doctoral theses. The findings indicate the potential underrepresentation of female scientists in pursuing interdisciplinary research at the early stages of their careers. Given that funding agencies have promoted interdisciplinary research and its potential benefits, the lower level of interdisciplinarity in the doctoral theses of female students may hinder their career advancement. Furthermore, our findings indicate that offering increased support to female faculty members may not only directly benefit their career development but also hold considerable significance in promoting future generations of female scientists. The findings of this study have important policy implications for advancing the careers of female scientists.