ノアピニオン氏の表題のブルームバーグ論説(原題は「Mergers Raise Prices, Not Efficiency」)やEquitablogで紹介されているが、オレゴン大のBruce A. BlonigenとFRBのJustin R. Pierceが「Evidence for the Effects of Mergers on Market Power and Efficiency」という論文を書き、NBERにも上げている

Study of the impact of mergers and acquisitions (M&As) on productivity and market power has been complicated by the difficulty of separating these two effects. We use newly-developed techniques to separately estimate productivity and markups across a wide range of industries using detailed plant-level data. Employing a difference-in-differences framework, we find that M&As are associated with increases in average markups, but find little evidence for effects on plant-level productivity. We also examine whether M&As increase efficiency through reallocation of production to more efficient plants or through reductions in administrative operations, but again find little evidence for these channels, on average. The results are robust to a range of approaches to address the endogeneity of firms’ merger decisions.