摘要
在過去的文獻上探討公司分割對母公司的宣告效果不勝枚舉。普遍來說，公司分割對於母公司而言是一件增加價值的決策，市場對其反應紛紛給予正向回應；然而，仍然有些公司會撤銷這件能增加公司價值的決策，甚為矛盾。故本研究即為探討撤銷公司分割背後的動機，以及其宣告時，市場對其反應。
學習效果與母子公司間的關係是可能促使公司決定撤銷分割的原因。根據本研究的羅吉斯迴歸分析結果得出，宣告公司分割時的累積異常報酬的多寡會影響公司日後決定撤銷的機率；當異常報酬越低，公司會越傾向撤銷，也就是說，公司學習市場反應，以決定策略。
此外，母子公司間的產業相關性也會影響公司決定撤銷與否。當母子公司同屬相關性產業時，其宣告分割時的累積異常報酬遠低於非相關性產業，因為其不具有集中效果（focus-increase）；而其撤銷分割的機率也較高。
本研究也對撤銷分割宣告時的市場反應進行研究，實證結果得知，宣告撤銷當天市場反應普遍給予負向回應，異常報酬為負。總而言之，市場對於公司分割給予正向肯定，而對於撤銷此決策則給予較負面的反應。

Abstract
The effects of spin-off announcement on parent firms have been discussed extensively in previous literature. Overall, the empirical evidence suggests that corporate spin-offs are value-increasing decisions for the parent companies. Nevertheless, an obvious paradox is that some spin-offs are withdrawn despite this value-creation attribute. In this research, we are examining the motivations behind this paradoxical event and observing the market response toward it.
Learning hypothesis and parent-subsidiary industrial relationship are the possible reasons. According to our logistic regression result, spin-offs announcement’s cumulative abnormal would have a big influence on the probability of withdrawn-spinoffs. The lower announcement cumulative returns are; the higher probability of withdrawal. Companies would learn from the market to make the most suitable decision.
Second, parent and spun-off firms’ industrial similarity or difference would also influence the chance of withdrawn spin-offs. When parent firm and spun-offs are in the related industry, their cumulative abnormal return in spin-offs announcement would be lower than in the unrelated industry which has focus-increase benefit. Therefore, the probability of withdrawal would be higher in order to correct the prior mistake.
Finally, we survey the outcomes of withdrawn spin-offs. In the announcement day (day zero), the abnormal return is negative significantly. Therefore, we could conclude that market reaction toward initial spin-offs is positive and toward the decision of canceling good news is negative on average. That is, market reaction toward withdrawn spin-off is negative.

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