本研究以聯立方程式法,配合事件研究法和Hausman外生性檢定(1978),探討在資訊不對稱情形下,年度盈餘宣告對股票價格、成交量、買賣價差之影響,並檢測這些反應之間是否具有互動關係?由於過去的研究,均假設這些反應彼此無關,多採用單一方程式法針對個別變數,分別探討盈餘宣告之資訊內涵(Atiaseand Bamber, 1994; Collerand Yohn, 1997; Loboand Tung, 2000),但盈餘宣告對三者之反應是同時決定且彼此交互影響,故單一方程式法可能會導致有偏且不一致的參數估計(Pindyck and Rubinfeld, 1998)。近來學者們亦逐漸採用聯立方程式法,此法對於變數交互影響的處理相較於傳統單一方程式法有其優越性。本研究嘗試運用聯立方程式法進行分析,以國內資訊電子業120家上市公司作為實證的研究對象,研究期間為民國89年1月1日至民國91年12月31日止,共計360個樣本。實證結果歸納如下:(1)公司宣告盈餘,在事件期中會增加買賣價差、成交量及累積異常報酬。(2)經由Hausman外生性檢定結果顯示,年盈餘宣告對買賣價差、交易量與股票報酬之影響是同步決定的,亦即以單一方程式法估計將產生偏誤及不具一致性的結果。(3)以三階段最小平方法(3SLS)估計研究模型,顯示在資本市場中,交易雙方面臨資訊不對稱的情形下,年度盈餘宣告對三者之影響是相互關聯的。
We use simultaneous-equation approach, event study analysis and Hausman Test for endogenity to examine the interactions of price, trading volume and bid-ask spreads on the earnings announcement. We select 120 from TSE sample stocks in Taiwan's electronics industry. The samples of our study contain 360 events during the period 2000/1/1-2002/12/31. The empirical result find that there are a growth in bid-ask spreads, trading volume and cumulative abnormal returns around earnings announcements. Further, the relations among bid-ask spreads, trading volume and stock returns around earnings announcements are simultaneous determined. The equation-by-equation estimation can lead to biased and inconsistent parameter estimates. From the 3SLS estimations, it is evident that when both trade sides under asymmetric information, the bid-ask spreads, trading volume and stock returns reactions to annual earnings announcements in the capital market are interrelated.