Rethinking Measures of Mergers & Acquisitions Deal Premiums
研究发现传统固定事件窗口（如-20、-42或-63天）会低估并购溢价最多8个百分点，尤其对目标方发起的长期交易偏差更严重。通过手工收集交易启动日期可纠正此偏差，并得出与现有文献矛盾的结论。
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.