This new paper by De Locker and Eeckhout will likely be classic:

We document the evolution of markups based on firm-level data for the US economy since 1950. Initially, markups are stable, even slightly decreasing. In 1980, average markups start to rise from 18% above marginal cost to 67% now. .. Increase in average market power .. can account for .. slowdown in aggregate output. .. The rise in market power is consistent with seven secular trends in the last three decades.

Yes, US public firms have only 1/3 of US jobs, and an even smaller fraction of the world’s. Even so, this is a remarkably broad result. I’d feel a bit better if I understood why their firm-level simple aggregation of total sales divided by total variable costs (their Figure B.5a) gives only a 26% markup today, but I’ll give them the benefit of the doubt for now. (And that figure was 12% in 1980, so it has also risen a lot.) Though see Tyler’s critique.

The authors are correct that this can easily account for the apparent US productivity slowdown. Holding real productivity constant, if firms move up their demand curves to sell less at a higher prices, then total output, and measured GDP, get smaller. Their numerical estimates suggest that, correcting for this effect, there has been no decline in US productivity growth since 1965. That’s a pretty big deal.

Accepting the main result that markups have been marching upward, the obvious question to ask is: why? But first, let’s review some clues from the paper. First, while industries with smaller firms tend to have higher markups, within each small industry, bigger firms have larger markups, and firms with higher markups pay higher dividends.

There has been little change in output elasticity, i.e., the rate at which variable costs change with the quantity of units produced. (So this isn’t about new scale economies.) There has also been little change in the bottom half of the distribution of markups; the big change has been a big stretching in the upper half. Markups have increased more in larger industries, and the main change has been within industries, rather than a changing mix of industries in the economy. The fractions of income going to labor and to tangible capital have fallen, and firms respond less than they once did to wage changes. Firm accounting profits as a fraction of total income have risen four fold since 1980.

These results seem roughly consistent with a rise in superstar firms:

If .. changes advantage the most productive firms in each industry, product market concentration will rise as industries become increasingly dominated by superstar firms with high profits and a low share of labor in firm value-added and sales. .. aggregate labor share will tend to fall. .. industry sales will increasingly concentrate in a small number of firms.

Okay, now lets get back to explaining these marching markups. In theory, there might have been a change in the strategic situation. Perhaps price collusion got easier, or the game became less like price competition and more like quantity competition. But info tech should have both made it easier for law enforcement to monitor collusion, and also made the game more like price competition. Also, anti-trust just can’t have much effect on these small-firm industries. So I’m quite skeptical that strategy changes account for the main effect here. The authors see little overall change in output elasticity, and so I’m also pretty skeptical that there’s been any big overall change in the typical shape of demand or cost curves.

If, like me, you buy the standard “free entry” argument for zero expected economic profits of early entrants, then the only remaining possible explanation is an increase in fixed costs relative to variable costs. Now as the paper notes, the fall in tangible capital spending and the rise in accounting profits suggests that this isn’t so much about short-term tangible fixed costs, like the cost to buy machines. But that still leaves a lot of other possible fixed costs, including real estate, innovation, advertising, firm culture, brand loyalty and prestige, regulatory compliance, and context specific training. These all require long term investments, and most of them aren’t tracked well by standard accounting systems.

I can’t tell well which of these fixed costs have risen more, though hopefully folks will collect enough data on these to see which ones correlate strongest with the industries and firms where markups have most risen. But I will invoke a simple hypothesis that I’ve discussed many times, which predicts a general rise of fixed costs: increasing wealth leading to stronger tastes for product variety. Simple models of product differentiation say that as customers care more about getting products nearer to their ideal point, more products are created and fixed costs become a larger fraction of total costs.

Note that increasing product variety is consistent with increasing concentration in a smaller number of firms, if each firm offers many more products and services than before.

Added 25Aug: Karl Smith offers a similar, if more specific, explanation.