With the growth of common ownership and investor engagement with portfolio firms, the possibility of adverse competitive effects of common ownership has become an important issue. To date, most of the focus has been on “unilateral” effects. In this Article, we shift the focus to the potential “coordinated” effects of common ownership and the appropriate antitrust treatment. After examining the ways in which a common owner could be a particularly effective cartel facilitator, we identify five scenarios, based on antitrust case law and enforcement experience, in which common ownership could plausibly increase the potential for coordinated conduct in concentrated markets. For each, we provide an economic analysis of the potential anticompetitive coordinated effects and we consider the appropriate legal treatment under Section 1 of the Sherman Act. The five scenarios are: Common Owners as Cartel Initiators; Common Owners as Trustworthy Conduits; a Common Compensation Structure as a Facilitating Practice; Common Owners as Brakes; and Common Owners as Vectors of Infection. We then turn to whether and how the anticompetitive potential for coordinated effects of common ownership might affect merger analysis under Section 7 of the Clayton Act or the EU Merger Regulation.

Recent empirical research purports to show that common ownership by institutional investors harms competition even when all financial holdings are minority interests. This research has received a great deal of attention, leading to both calls for and actual changes in antitrust policy. This paper examines the research on this subject to date and finds that its conclusions regarding the effects of minority shareholdings on competition are not well established. Without prejudging what more rigorous empirical work might show, we conclude that researchers and policy authorities are getting well ahead of themselves in drawing policy conclusions from the research to date. The theory of partial ownership does not yield a specific relationship between price and the MHHI. In addition, the key explanatory variable in the emerging research - the MHHI - is an endogenous measure of concentration that depends on both common ownership and market shares. Factors other than common ownership affect both price and the MHHI, so the relationship between price and the MHHI need not reflect the relationship between price and common ownership. Thus, regressions of price on the MHHI are likely to show a relationship even if common ownership has no actual causal effect on price. The instrumental variable approaches employed in this literature are not sufficient to remedy this issue. We explain these points with reference to the economic theory of partial ownership and suggest avenues for further research.

Recent years have witnessed an increased interest, by competition agencies, in assessing the competitive effects of partial acquisitions. We propose an empirical structural methodology, which can deal with settings involving all types of owners and ownership rights, to quantify the coordinated effects of partial horizontal acquisitions on differentiated products industries, by evaluating the impact of such acquisitions on the minimum discount factors for which coordination can be sustained. We also provide an empirical application of the methodology to several acquisitions in the wet shaving industry that give rise to cross- and common-ownership structures. The results are as follows (i) the incentives to coordinate of the firms that the acquiring party is - pre-acquisition - able to influence are non-decreasing with any acquisition; (ii) the incentives to coordinate of the acquired firm are non-decreasing with acquisitions involving full or partial both financial and corporate control rights, but non-increasing with acquisitions involving full or partial solely financial rights; and (iii) the incentives to coordinate of the remaining firms in the industry are non-increasing with any acquisition. This implies that the coordinated effects of partial horizontal acquisitions are, in general, ambiguous, which illustrates the importance of an empirical structural methodology.

Kennedy, O'Brien, Song, and Waehrer (2017) replicate the panel results of Azar, Schmalz and Tecu (forthcoming), but argue on theoretical grounds that the estimates should not be interpreted as anti-competitive effects of common ownership. They then develop and estimate alternative models and find no significant positive effects of common ownership on airline ticket prices. This note points out features of their empirical analysis that cast doubt on the reliability of their method and results. Their conclusion that the data do not support AST's interpretation seems unwarranted.

The current debate on the competitive risks of common ownership has focused on whether passive index investments soften competition among portfolio companies. However, even if one concedes, in arguendo, that this is the case, it remains unclear in what way this bears on the analysis of horizontal mergers between portfolio companies. The EU Commission in Dow/DuPont and Bayer/Monsanto has alleged that common ownership is “an element of context in the appreciation of any significant impediment to effective competition”. In that respect we hypothesize that it should not be presumed that common ownership in itself increases anticompetitive effects of a merger between portfolio companies. Instead we posit that this depends on the facts of the case. The existence of common ownership might even mitigate post-merger unilateral effects if compared to the pre-merger counterfactual. We test our hypothesis on price competition as well as on innovation competition. Eventually, we map our conclusions onto the legal principles governing the burden of proof in merger cases.

The potentially anticompetitive effects of common ownership are being discussed controversially. While the US agencies still display reluctance, the Commission has already invoked common ownership has part of a theory of harm in Dow/DuPont and Bayer/Monsanto. In our paper we focus on how common ownership can bear on the application of price pressure indices in unilateral effects analysis of horizontal mergers between portfolio companies. We do not assess whether the underlying premise of common ownership to lead to an internalization of shareholders' expectations of high overall market returns is convincing. Rather, we hypothesize such common shareholder influence. Our main conclusion is that common ownership should still not be considered a general circumstantial factor indicating competitive harm with respect to post-merger price increases or effects on innovation competition. Rather, it calls for case-by-case analysis.