Through studying the changes in stock price during the time before and after the event, not only the influence of a certain event can be estimated but also the validity of market can he tested.

• 事件研究是一种重要的研究方法，通过对事件发生前后一段时间内股票价格变化的研究，既可以估计某一特定事件的影响程度，也可以检验市场的有效性程度。