Merger Retrospective Studies: a Review
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COVER STORIES Antitrust , Vol. 23, No. 1, Fall 2008. © 2008 by the American Bar Association. Reproduced with permission. All rights reserved. This information or any portion thereof may not be copied or disseminated in any form or by any means or stored in an electronic database or retrieval system without the express written consent of the American Bar Association. Merger Retrospective Studies: A Review BY GRAEME HUNTER, GREGORY K. LEONARD, AND G. STEVEN OLLEY HETHER THE ANTITRUST public data sources, either because of regulation (e.g., airlines) agencies during the Bush administration or for marketing reasons (e.g., consumer products). were setting appropriate thresholds for Most retrospective merger studies have focused on price. merger review has become a subject of However, it is important to note that price is not the only Wintense debate. 1 An outcome of this debate competitive variable that can be affected by a merger. A has been a widespread call to evaluate merger policy using merger’s competitive effects may well extend to product studies that retrospectively analyze the actual competitive improvements, new product introductions, advertising and effects of consummated mergers. 2 Information about the promotion, repositioning of existing products, etc. All else actual competitive effects of mergers and other transactions equal, the total competitive effect can be determined by ana - that have been permitted by the agencies can help in evalu - lyzing quantity (or share) changes. 5 Several of the studies we ating whether the agencies are setting appropriate thresholds discuss below analyze share in addition to price. for challenging mergers. As Dennis Carlton has pointed out, Some retrospective merger studies have evaluated the this is particularly true if the actual competitive effects can be effects of mergers on the costs of the merging parties. Because compared to the agencies’ pre-merger predictions of those efficiencies claimed by the parties are often a subject of con - effects. 3 tention during merger reviews, the studies that have ana - A merger retrospective study necessarily can analyze only lyzed whether mergers have actually delivered efficiencies are those mergers that have actually occurred. For the most part, particularly valuable. this means that mergers included in a retrospective study are In this article, we review various merger retrospective stud - those that were cleared by the agencies. 4 That the sample of ies that have appeared since 1990 (although some of these cleared mergers is not a random sample of all mergers is obvi - studies address mergers that took place in the 1980s). While ous. Less obvious is that the sample of mergers studied by we focus primarily on studies that have appeared in the tech - researchers is likely not a random sample of all cleared merg - nical economics literature, we also describe some less formal ers. With a few exceptions, researchers conducting retrospec - studies. 6 tive merger studies have tended to focus on controversial The existing merger retrospective studies that we discuss “marginal” cases. While it is human nature to want to resolve below address mergers that span a period of over twenty a controversy, researchers have also done a valuable service. To years. During that time, the technical tools and approaches improve agency decision making, an understanding of what the agencies use to analyze mergers have evolved substantial - transpired in a marginal case is often much more useful than ly, and the enforcement philosophy of the agencies may have an understanding of what transpired in a non-marginal case. shifted over time with different presidential administrations. Nevertheless, it is important to recognize that the results There are far too few retrospective merger studies to make from merger retrospective studies generally describe the com - any assessments as to whether agency enforcement in any one petitive effects of the marginal merger, not the “average period was too restrictive or too lax. cleared merger,” let alone the “average proposed merger.” To summarize our discussion below, the majority of stud - Besides being limited to consummated mergers, retro - ies that analyze price effects have found post-merger price spective merger studies have also been limited in their indus - increases. A significant minority of studies have found no try scope by data availability. Analyzing the effects of a merg - price effects. This is perhaps the expected result when retro - er typically requires detailed data on prices, costs, and other spective merger studies focus on marginal mergers, and often economic conditions both before and after the merger. For controversial mergers at that. The studies that have analyzed most mergers, such data are not readily publicly available. cost changes have found that the mergers studied achieved Most studies have been done in industries for which there are substantial cost-savings. Difference-in-Differences Methodology Graeme Hunter and Steven Olley are Vice Presidents at NERA Economic Given that a common theme among merger retrospective Consulting. Gregory K. Leonard is a Senior Vice President at NERA studies in the economics literature is the use of the difference- Economic Consulting and an Associate Editor of A NTITRUST . The authors thank Ariella Karshan for research assistance. in-differences (DID) approach for estimating the effect of a merger, we provide an introduction to that methodology at 34 · ANTITRUST the outset. 7 Done properly, a DID analysis is a useful tool for decide to merge because they believe a merger would allow establishing the competitive effects of a merger. The starting them to offset this price decrease and thereby maintain their point for understanding DID is the familiar “before-after” prices. Then, the DID approach would mistakenly conclude comparison, whereby prices before an event such as a merger that the merger had no effect (both the control and affected are compared to prices after the event. For example, the prices products would show no price change post-merger). of the merging companies’ products before and after the merg - The DID approach as described above can be augmented er might be compared. However, this simple before-after com - by controlling in a regression framework for the economic parison for the potentially affected products or geographic factors specific to, respectively, the affected and control areas areas does not control for changes in other economic factors or products. This provides a further ability to isolate the that occurred between the before and after periods. While in effect of the merger. some cases it might be possible to control for changes in Economists have used the DID approach in a wide vari - observable economic factors by including such factors in a ety of contexts, such as program evaluation. 8 In antitrust, cer - regression model, there may be other economic factors that are tain familiar types of analyses are actually examples of the unobservable and thus not readily controlled for in this way. DID methodology. For example, regression analyses of the DID provides a way to control for changes in economic price effects of entry, such as those used in the Whole Food s 9 factors other than the merger. It does so by identifying a “con - and Staple s 10 cases, employ cities without entry as a control trol” product or geographic area for which price is affected by for cities with entry. This is just a form of DID. We describe the other economic factors, but not by the merger itself. Thus, in detail below how merger retrospective studies have used the change in price in the control area or product before and the DID methodology to analyze the effects of mergers. after the merger provides a measure of the effect of the other economic factors. This price change for the control can then The Oil and Gas Industry be subtracted from the price change in the affected area or The oil and gas industry has provided the basis for several product and one can assess the impact of a merger by analyz - merger retrospective studies. Two recent studies of specific ing relative price changes before and after a merger. transactions were conducted by Taylor and Hosken 11 and For example, suppose that a merger between two com - Simpson and Taylor. 12 In addition, the U.S. General panies affects customers for the product in St. Louis but not Accounting Office (GAO) conducted a stud y13 that assessed Omaha, while the prices for the product in St. Louis and the price effect from eight different mergers simultaneously, Omaha would otherwise move together (i.e., are highly cor - including the two mergers analyzed by Taylor and Hosken related) due to common supply and demand conditions. and Simpson and Taylor. Thus, Omaha can serve as a good control for St. Louis. Fur- Taylor and Hosken addressed the price effect of the 1997 ther assume that, in the period after the merger, the price in joint venture agreement between USX-Marathon Group and both St. Louis and Omaha increased by 10 percent due to Ashland Inc., which combined the downstream refining and common increases in cost and demand, but the price in St. marketing operations of the two companies. The joint ven - Louis increased by an additional 5 percent due to the merg - ture, Marathon Ashland Petroleum (MAP), combined four er. A simple before-after comparison in St. Louis would Marathon refineries with three Ashland refineries. In addi - yield a price change of 15 percent, which would substantially tion, Marathon contributed 51 wholesale terminals and 3,980 overstate the 5 percent effect of the merger. Only by sub - retail outlets and Ashland contributed 33 terminals and 1,420 tracting the 10 percent price change observed in Omaha (the retail outlets. 14 control area) from the 15 percent price change observed in Taylor and Hosken analyze the competitive effects of this St.