Is the event study methodology useful for merger analysis? A comparison of stock market and accounting data

This paper presents empirical evidence about the ability of event studies to capture mergers' ex-post profitability as measured by accounting data. We use a sample of large horizontal concentrations during the period 1990-2002 involving 482 firms either as merging firms or competitors, and contrast a measure of the mergers' profitability based on stock market event studies with one based on balance sheet profit data. We show that using a long window around the announcement date (25 or 50 days before the event) increases the ability to capture the ex-post merger effect: the pairwise correlation coefficient is positive and highly significant.