One implication is that income inequality isn’t quite as extreme as measured. Another implication is that rising income inequality will itself cause higher mark-ups, but without the economy becoming “more monopolistic” per se. Here is the paper:
The Law of Diminishing Elasticity of Demand (Harrod 1936) conjectures that price elasticity declines with income. I provide empirical evidence in support of Harrod’s conjecture using data on household transactions and wholesale costs. Over the observed set of purchases, high-income households pay 9pp higher retail markups than low-income households. Half of the differences in markups paid across households is due to differences in markups paid at the same store. Conversely, products with a high-income customer base charge higher markups: a 10pp higher share of customers with over $100K in income is associated with a 2.5–5.2pp higher retail markup. A search model in which households’ search intensity depends on their opportunity cost of time can replicate these facts. Through the lens of the model, changes in the income distribution since 1950 account for a 9pp rise in retail markups, with one-third of the increase due to growing income dispersion. This rise in markups consists of within-firm markup increases as well as a reallocation of sales to high-markup firms, which occurs without any changes to the nature of firm production or competition.