Effect of R&D and Market Concentration on Merger Outcomes -- An Event Study of US Horizontal Mergers

<title>Abstract</title> This study examines the pattern of abnormal returns for merging companies and rivals, to determine investor expectations regarding the impact of horizontal mergers challenged by the government. Prior studies have indicated that the government may have challenged efficiency-enhancing mergers, as evidenced by the pattern of abnormal returns to rivals during merger events. This study uses a two-stage regression approach to examine those patterns, using challenged mergers from 1997 to 2007, and finds evidence of potential price effects from approved mergers. The results also show the mergers to have differential effects depending on the level of R&D, market concentration, and product sales.