The UK gender pay gap: Does firm size matter?

Motivated by the introduction of the UK Gender Pay Gap Reporting legislation to large firms, defined as over 250 employees, we use linked employee-employer panel data from the Annual Survey of Hours and Earnings to explore pre-legislation variation in the gender pay gap by firm size. In doing so, we contribute to the evidence on the relationship between two prominent empirical regularities in the labour economics literature, namely the gender pay gap and the firm-size wage premium. We find that both the raw and adjusted gender pay gaps increase with firm size in the UK private sector, even after controlling for unobserved worker heterogeneity, consistent with the legislation being targeted effectively. However, this conclusion changes after accounting for unobserved firm-level heterogeneity. Large firms have smaller within-firm raw gender pay gaps and similar adjusted gender pay gaps when compared to smaller firms. Our findings are not specific to the current definition of large firms but hold more generally, including at alternative proposed size thresholds.