Two Components of Wage Gaps Induced by Individual-level Variables: Intra-firm or Inter-firm?

Individual-level variables such as gender, education, occupation, and employment type are well-known factors that induce wage gaps in the labor market. This article aims to divide wage gaps into two components—those arising within each firm (the intra-firm wage gap) and those arising between different firms (the inter-firm wage gap)—and measure their respective proportions by individual-level variables, as studies suggest that each wage gap based on an individual-level variable has a unique mix of an intra-firm and inter-firm wage gap. This measurement can help enrich investigation into the generative process of wage gaps and formulate effective labor policies to reduce them. Accordingly, we compared the coefficients of the independent variables of the wage function estimated by a pooled ordinary least squares model and a fixed-effect model, using nationwide employer–employee matching data collected by the Japanese government. We found that wage gaps by gender and employment type mostly consist of intra-firm wage gaps, and those by education and occupation have a larger share of inter-firm wage gaps. The findings suggest that different research strategies are required to investigate the generative process of each wage gap, and that regulations on and interventions in organizational processes are important to reduce wage gaps based on gender and employment type.