Post-merger Price Variation Matters, So Why Do Merger Retrospectives Ignore It?

Abstract

The price effect of past mergers has been extensively researched over the past two decades. The overwhelming majority of these studies estimate the over-time average price effect of the merger. Merger guidelines agree that mergers should be approved if market dynamics, such as entry, eliminate negative welfare effects. Estimating price averages ignores key information about the post-merger dynamics of prices and is unable to identify if post-merger prices eventually revert to pre-merger levels. We provide evidence from a set of Monte Carlo experiments to show how serious this problem might be. Firstly, potentially all the studies that concluded - estimating post-merger over-time averages - that the merger led to a price increase, could have been wrong, and in fact the merger price increase disappeared within a reasonable time. Similarly, up to half of the studies that concluded that the merger did not increase prices could have been wrong in their conclusion.