摘要

1997年亞洲金融危機發生，國際資金的快速移動，造成外匯市場和股票市場巨大的震盪，特別是股票市場的波動會影響財富的價值，進而影響消費和投資的決定，以及實質的經濟活動。因此，股價波動成為近幾年來文獻上探討的主題，本文建構一理性投機的隨機模型，從理論上探討股票市場的波動。
當討論到股票市場的波動時，常常會認為股價的劇烈波動是由於非理性的投機者追高殺低所造成的。但根據Friedman (1953)的論點，若市場上存在投機者，則只有擁有成功策略的理性投機者能存活，而且這些理性投機者將不會造成市場波動。在此，顯現了一個令人關心的議題，是否理性投機者會因某些情況而使股價波動劇烈呢? 因此，理性投機者在市場中的角色有必要深入探討，尤其在國際資金快速移動的時代，外資的角色更是不容忽視。有鑑於此，本文也將探討外資的角色。
本文的研究結果發現，當經濟體系發生短暫性的外生衝擊，導致長期和短期的股價存在價差，理性投機者預期股價會回復長期均衡值，而進場買賣以套取價差時，此種套取價差的行為能使股價穩定。但是，若此一衝擊同時使得理性投機者面臨有額外的損失或利得，因而調整其應持有的部位，則最後將有可能使得股價的波動變大。因此，理性投機的外資可能穩定股市，也可能是股市波動的來源。

參考文獻

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