The mediator effect of STEM education on the gender pay gap: a case study of early-career graduates at a Southern Italian university

Despite recent progress towards a more balanced work environment in terms of gender, the Gender Pay Gap is still a widespread relevant issue both from the economic and sociopolitical points of view. This paper focuses on Italy and uses AlmaLaurea survey data on University of Palermo graduates one year after graduation. The aim is to investigate the potential mediator role of the field of study (STEM vs non-STEM) in the Gender Pay Gap. In fact, the low participation of female students in STEM fields, known to be the most remunerative fields, could partially explain the difference in the average monthly salary of the graduates. In this paper, we adopt a causal mediation framework with Propensity Score Weighting to address selection bias due to the observational nature of the study. We then employ quantile regression to capture heterogeneity across the salary distribution. Results, on the one hand confirm the well-known discrimination in salary between males and females, suggesting that structural and cultural barriers persist, on the other hand highlight the mediation role of the degree type. STEM degrees seem to give a consistent salary premium, particularly in the lower and middle quantiles of the salary distribution, significantly mediating the salary advantage of men. These findings underscore the need for policies that both promote women’s access and retention in STEM education and address broader institutional and cultural sources of salary inequality.