指數成分股調整效應是行為財務領域的一大研究課題。近年來隨著中國股市不斷發展，各類指數衍生品層出不窮，指數的編制和調整也就產生越來越大的影響。另一方面，中國股市仍屬於新興市場，指數成分股調整的效應相較國外發達市場也許存在其特殊之處。而面對這一重要課題，中國學界和業界的研究卻略顯不足。鑒於此，本文從短期和長期兩個角度來研究對中國股市影響最大的指數——滬深300指數的成分股調整效應。 在滬深300指數成分股調整的短期效應方面，本文從股價和成交量兩個方面進行了研究。實證結果顯示，在股票剛被調入指數後，股價會產生正的異常報酬且成交量上升，而被調出指數的股票成交量會略微上升且產生負的異常報酬。但是與國外的實證結果相比，滬深300指數成分股調整的短期效應並沒有非常明顯，本文認為這可能與中國股市機構投資人占比過少有關。 在指數成分股調整對調入股和調出股的長期影響方面，本文首先研究了指數調整後的長期股價表現，發現調入股的股價累積報酬優於指數，但不如調入指數前自身的股價表現，調出股則與之相反。接著對股東人數、機構投資人數量和股價波動度進行比較分析。研究發現，指數調整之後，調入股的股東人數會顯著上升，調出股的股東會減少，但該因素對指數調整後股票的長期異常報酬沒有明顯影響；指數成分股調整後機構投資人數量和股價波動度也有明顯變化——調入股的機構投資人增加，波動度降低，調出股機構投資人減少，波動度上升——且這兩個因素對股價異常報酬的影響是顯著的。另外，公司規模大小也是影響股價異常報酬的一個顯著因素。 / The effect of stock index composition changes is one of the important subjects in the field of behavioral finance. With the rapid development of Chinese equity market, stock index is playing an increasingly important part. Chinese equity market, on the other hand, is still at emerging stage, the stock index composition changes may have the different effect from that of the developed countries. However，the correlative study in China is far from enough. This paper investigates the CSI 300 which is the most influential stock index in China to find out the the effect of stock index composition changes in both short term and long term. In the short term, the study focuses on the price and volume. The empirical results show that there is a positive abnormal returns and increasing trading volume of added firms, while a negative abnormal returns and slightly increasing trading volume of deleted firms. However, compared with empirical results abroad, short-term effects associated with the change of the CSI 300 index list is not very obvious, which may be accounted for too little institutional investors in the Chinese stock market. In the long term, this paper firstly studies the long-term stock price performance of the index adjustment. For additions, cumulative return after index adjustment is better than that of the CSI 300 index, but is worse than the performance before the adjustment, while the deletions performance is opposite. Secondly, number of shareholders, institutional investors and stock price volatility are analyzed. There is a significant increase in the number of shareholders of added firms and a decline for deleted firms, but this factor has little influence for abnormal stock price returns. Similarly, for additions, institutional investors increases and volatility reduces, deletions are opposite. Abnormal stock price returns are significantly affected by the number of institutional investors and volatility. In addition, the company size is also a significant factor affecting the abnormal returns.

指數效應是指當股票調入或調出某個指數的時候，該股票的價格及成交量所出現的異常反應。這種有悖於市場有效性的金融現象廣受學者和投資者的關注，國外學者對指數效應的研究已較為成熟，形成了價格壓力假說、流動性假說、向下傾斜的需求曲線假說、資訊含量假說以及市場區隔假說等5種用於解釋這一現象的理論假說。 中國指數的發展較晚，所以學者對其指數效應的研究還不夠完善。本文以2006年至2015年滬深300指數調入和調出股票為研究對象，利用事件窗研究法檢驗股票的價格效應和成交量效應是否存。本文發現滬深300指數調入和調出股票的指數效應顯著，且具有不對稱性。調入股票的正異常報酬長期存在且不反轉，而調出股票出現的負異常報酬短期內會反轉為正，且反轉後在長事件窗內累計異常報酬甚至高於調入股票；調出股票的平均交易比率也要比調入股票更為顯著且活躍。 本文研究指出，歸因於指數基金追蹤行為的價格壓力假說與向下傾斜的需求曲線假說只能部分的解釋滬深300指數效應。因此本文將調入和調出股票價格效應不對稱性與公司基本面的研究相結合，通過分析滬深300指數調整後調入和調出股票的EPS預測值、實際EPS的變動、分析師覆蓋以及機構投資者數量證實了資訊含量假說以及市場區隔假說的解釋力。本文以長期累計異常報酬對流動性假說、資訊含量假說和市場區隔假說中各個經典指標進行多元迴歸分析，發現指數成分股調整前後EPS的變動可以解釋調入股票和調出股票價格效應的存在性和不對稱性，此外資訊含量假說對滬深300指數效應的解釋力度相對較大。由此證明了滬深300指數調整隱含有關公司基本面的額外資訊。