Rethinking Measures of Mergers & Acquisitions Deal Premiums

Abstract Many academic studies use fixed preannouncement event days (e.g., -20,-42, or -63) to measure takeover premiums. In this paper, we show that the use of traditional fixed windows generates premiums that are underestimated by as much as 8 percentage points. This downward bias is especially severe for transactions with long processes (e.g., target-initiated deals). We take account of this bias by hand collecting deal initiation dates and show that using these dates results in measured premiums that give contradictory conclusions to those found in existing literature. We also offer guidance for measuring premiums if hand collecting data is impractical.