We study how the courts have responded to the 2010 Horizontal Merger Guidelines issued by the U.S. Department of Justice and the Federal Trade Commission. Looking at decided cases, we find that both the government and merging parties rely on the 2010 Guidelines in presenting their cases, each side respectively arguing that it should win if the court properly follows them . The 2010 Guidelines had the strongest effect on the case law in the area of unilateral effects, where a number of courts have embraced them in ways that clearly depart from earlier decisions. The case law now exhibits much greater receptivity to a government showing that the merger will lead to higher prices simply due to the loss of direct competition between the two merging firms. The courts also have followed the 2010 Guidelines by more willingly defining markets around targeted customers. We do not detect any effect on decided cases of the higher concentration thresholds found in the 2010 Guidelines. Both the average pre-merger level of market concentration and the average increase in market concentration alleged by the government in litigated cases to date declined after 2010 .

我们研究了法院如何回应美国司法部和联邦贸易委员会发布的2010年横向并购指南。在审理已决案件时，我们发现政府和合并方在提出案件时都依赖《 2010年指南》，双方分别辩称，如果法院正确地遵循它们，则胜诉。在单方面影响方面，《 2010年指南》对判例法的影响最大，在该方面，许多法院以明显背离先前判决的方式接受了这些判决。判例法现在对政府表现出更大的接受度，表明合并仅由于两个合并公司之间直接竞争的丧失而将导致更高的价格。法院还遵循《 2010年指南》，更乐意围绕目标客户定义市场。对于2010年指南中确定的更高浓度阈值的确定案例，我们没有发现任何影响。迄今为止，政府在诉讼案件中声称的平均合并前市场集中度和平均市场集中度均在2010年之后下降。