Why do the earnings of male and female graduates diverge? The roles of field of study, motherhood, and job dynamics

Abstract This article investigates the dynamics of the gender pay gap using an administrative dataset of Irish graduate earnings. Although male and female graduates have similar earnings initially, a substantial gap emerges in the 10 years after graduation. We focus on three possible sources: childbirth, field of study, and job mobility. We find that the gap is driven by the earnings of mothers, which fall by 24 per cent relative to trend immediately after childbirth and this effect is evident for all field groupings. We examine and dismiss the possibility that the gender difference is driven by job mobility; in fact, almost all the difference arises for job stayers. Although there is a large and persistent reduction in average hours of work after childbirth, this does not seem to explain all of the emerging gap. Our results suggest that policy measures should focus on earnings dynamics within firms.