Over the past decade, the US economy has been plagued by sluggish wage growth and rising income inequality. The debate over inequality in the 1980s and 1990s focused on the growing disparity between the earnings of skilled and unskilled workers and the earnings of the super-rich. Growing inequality between capital and labor income has now been added to these concerns. Remarkably, the growth in real GDP per worker over the decade of the 2000s, which averaged 1.7 percent annually, was actually more rapid than in the 1970s, 1980s, or 1990s, yet in the 2000s workers saw almost no increase in their take-home pay. Consistent with this gap between labor productivity and wage growth was a pronounced decline in the share of US national income earned by workers. As labor's share has declined, the share of capital has risen and has been especially concentrated in corporate profits. As profits are far less equally distributed than wages, this increase has contributed to rising income inequality. There are several plausible reasons for this development—globalization, automation, weak bargaining power of labor, political capture, higher markups—but the natural starting point for explaining factor income shares is the neoclassical theory of the functional distribution of income enumerated by John Hicks and Joan Robinson in the 1930s. In this framework there are two possible explanations for labor's recent declining share. The first is that capital and labor are gross substitutes, and the second is that capital and labor are gross complements. Several papers have explained the recent decline in labor's share in income by claiming that capital has been substituted for labor. Lawrence puts forward the alternative "gross complements" explanation for the declining US labor share. He shows that despite a rise in measured capital-labor ratios, labor-augmenting technical change in the United States has been sufficiently rapid that effective capital-labor ratios have actually fallen in the sectors and industries that account for the largest portion of the declining labor share in income since 1980. In combination with estimates that corroborate the consensus in the literature that the elasticity of substitution is less than 1, these declines in the effective capital-labor ratio can account for much of the recent fall in labor's share in US income at both the aggregate and industry level. Paradoxically, these results also suggest that increased capital formation, ideally achieved through a progressive consumption tax, would raise labor's share in income.
Data disclosure: The data underlying the figures in this analysis are available here [xlsx].