本文以事件研究法檢視2011 年5 月23 日爆發的塑化劑事件對台灣食品、生化醫療類股與相關個股異常報酬率的影響，並輔以連檢定檢視異常報酬率是否仍呈現隨機波動的模式。 實證結果指出，上市(櫃)公司生技醫療類股和上市公司食品類股的逐日累積異常報酬率多為負數，卻不具統計顯著性，惟三者均呈現下移的系統性變動；產品遭受塑化劑污染的生技醫療和食品上市公司個股的平均累積異常報酬率除事件日後第2 日至第4 日不顯著外，第1 日和第5 日至第30 日均為負數，且均通過5%之顯著性檢定。值得注意的是第26 日的平均累積異常報酬率降到最低，達-0.13074，表示塑化劑事件讓八家上市公司的價值平均減少了13.074%，顯然投資人對塑化劑事件有相當強烈的負面反應。

This study investigates the impact on the abnormal returns of the food processing and biomedical industries as well as the individual companies involved in the event of the plasticizer event that occurred on May 23rd, 2011. The methods used in this study include the event study and the runs test. The latter is employed to examine whether the abnormal returns follow the stochastic pattern in the event window. Evidence indicates that, in the event window, none of the daily cumulative abnormal returns for the food processing and biomedical industries are statistically significant, though most of them are negative. They, however, display a positive serial correlation with a downward movement in the event window. The average cumulative abnormal returns for those companies involved in the plasticizer event are found to be statistically significantly negative at the 5% for the 1st day and the 0.1% for those period from the 5th day through the 30th day after the occurrence of the event. It is also found that the value of the companies shrinks, on the average, by 13.074% on the 26th day due to the plasticizer event. It is thus evident that the plasticizer event caused a dramatic reaction in the food processing and biomedical stock markets in Taiwan.