Equilibrium Wage Dispersion: Monopsony or Sorting?

Why are similar workers paid differently? I review and compare two lines of research that have recently witnessed great progress in addressing “unexplained” wage inequality: (i) worker unobserved heterogeneity in, and sorting by, human capital; (ii) firms’ monopsony power in labor markets characterized by job search frictions. Both lines share a view of wage differentials as an equilibrium phenomenon. Despite their profound conceptual and technical differences, they remain natural competitors in this investigation. Unlike other hypotheses, they provide natural and unifying explanations for job and worker flows, unemployment duration and incidence, job-to-job quits, and the shape of the wage distribution.