というNBER論文が上がっているungated版)。原題は「Declining Competition and Investment in the U.S.」で、著者はGermán Gutiérrez、Thomas Philippon(いずれもNYU)。

The U.S. business sector has under-invested relative to Tobin's Q since the early 2000's. We argue that declining competition is partly responsible for this phenomenon. We use a combination of natural experiments and instrumental variables to establish a causal relationship between competition and investment. Within manufacturing, we show that industry leaders invest and innovate more in response to exogenous changes in Chinese competition. Beyond manufacturing we show that excess entry in the late 1990's, which is orthogonal to demand shocks in the 2000's, predicts higher industry investment given Q. Finally, we provide some evidence that the increase in concentration can be explained by increasing regulations.

Equitable Growthでこの論文の紹介記事が出ているが、そこでは以下のように解説している。

They employ a so-called natural experiment where the entrance of competition from China changed investment decisions in the manufacturing sector, which is likely to generate clear results. The two economists then ran an analysis that looks at how more firms entering an industry than expected affects competition and then investment. This technique isn’t going to be as crisp or clear as a natural experiment, but it’s likely to be a general result that holds up in a number of cases.
...Furthermore, other research by Gutiérrez and Philippon shows that investment in the United States is weaker than in Europe, where competition is higher. The case that declining competition is causing, at least in part, the reduction in investment growth seems quite strong.
If this is the case, then the question is: What’s causing this decline in competition? The two economists look at three potential explanations: increasing regulation; the rise of “superstar” firms; and an aging U.S. population. They find a fair amount of evidence for the role of regulation, slightly less for superstar firms, and not much evidence at all for changing demographics.
彼らの説が正しければ、次の疑問が生じる:何が競争の低下をもたらしているのか? 2人の経済学者は3つの説明候補を調べた:規制の強化、「スーパースター」企業の台頭、米国民の高齢化である。彼らは規制の役割については相当量の証拠を見い出した。スーパースター企業についての証拠はそれよりやや少なかった。人口動態の変化についてはほとんど証拠を見い出さなかった。

なお、今回の論文は同じ著者の昨年末の論文「Investment-less growth: An empirical investigation」のフォローアップという位置付けになっている。以下はその先行論文の要旨*2

We analyze private fixed investment in the U.S. over the past 30 years. We show that investment is weak relative to measures of profitability and valuation – particularly Tobin’s Q, and that this weakness starts in the early 2000’s. There are two broad categories of explanations: theories that predict low investment because of low Q, and theories that predict low investment despite high Q. We argue that the data does not support the first category, and we focus on the second one. We use industry-level and firm-level data to test whether under-investment relative to Q is driven by (i) financial frictions, (ii) measurement error (due to the rise of intangibles, globalization, etc), (iii) decreased competition (due to technology or regulation), or (iv) tightened governance and/or increased short-termism. We do not find support for theories based on risk premia, financial constraints, or safe asset scarcity, and only weak support for regulatory constraints. Globalization and intangibles explain some of the trends at the industry level, but their explanatory power is quantitatively limited. On the other hand, we find fairly strong support for the competition and short-termism/governance hypotheses. Industries with less entry and more concentration invest less, even after controlling for current market conditions. Within each industry-year, the investment gap is driven by firms that are owned by quasi-indexers and located in industries with less entry/more concentration. These firms spend a disproportionate amount of free cash flows buying back their shares.

*1:論文のタイトルは「Is there an investment gap in advanced economies? If so, why?」。なお、こちらはアムステルダム大のRobin Döttlingが著者に加わっている。