Security Transaction taxes have been in place in many countries for many years now. Yet we do not fully know how these taxes effect prices, volumes, bid-ask spreads and volatility and in turn if they are good for the economy or not. This paper is an attempt to understand how security transaction taxes decrease volume of trading, decrease prices of stocks and increase bid-ask spreads. It analyses the effect the STTs implemented by the state and federal government in New York on June 1st 1905 and December 1st 1914 respectively, had on the stocks of the New York Stock Exchange. These results will help us analyze whether future implementations of STTs will harm or benefit the market.

本文使用 1981 年 1 月 5 日至 1997 年 5 月 31 日台灣加權股價指數以及交易股數的資料探討台灣股市的時間序列特性，並且針對政府對股市的干預政策檢定政策干預的有效性。本文採用的實證方法包含 Augmented Dickey-Fuller(ADF)單根檢定，Perron 結構性改變檢定， ARCH 效果檢定，干預分析(Intervention Analysis)以及 Granger 因果關係檢定。實證檢定的結果如下： 1、在單根檢定方面，股價指數、交易股數和股價指數變異數三個時間序列都是一階穩定序列。 2、在 Parron 結構性改變檢定方面，股價指數、交易股數和股價指數變異數三個時間序列在 1990 年 5 月到 10 月之間曾經發生明顯的結構性改變。 3、在 ARCH 效果檢定方面，股價指數和交易股數二個時間序列的殘差項都有 ARCH(1)效果存在，而股價指數變異數的殘差項不存在 ARCH(1)效果。 4、在干預分析方面，穩定基金對股價指數的干預效果不顯著。 在漲跌幅限制方面，漲跌幅限制的變動對股價指數、交易股數及股價指數變異數的干預效果都不明顯。 在證卷交易稅稅率改變的干預分析方面，證卷交易稅稅率改變對交易股數和股價指數變異數沒有影響，但是證交稅稅率變動和股價指數呈現正向的關係。 5、在 Granger 因果關係檢定方面，本研究發現漲跌幅限制改變和股價指數漲跌二者互為因果，但是股價指數對漲跌幅的影響較大。 在證卷交易稅稅率改變與股市的因果關係方面，本研究發現股價指數的漲跌是證交稅稅率改變之因，顯示主管機關的證交稅稅率政策是受股市的市場狀況所左右。 / In this paper, I examine the effectiveness of official intervention in Taiwan's equity market. I consider the security transaction tax, price limit and stabilization funds as examples. The nonstationarity and structural changes of equity index time-series process were first detected and detrended. The Autoregressive Conditional Heteroskedasticity (ARCH) model is employed to examine the intervention effectiveness, since it allows for a formal test of changes in the index mean level, index conditional variance or both, in response to the changes of security transaction tax and price limit. The results implies that policy authority adjusted security transaction tax and price limit in accordance to the change of equity index level. I also find that the imposition of security transaction tax and price limit have no significant effect on reducing the equity index volatility.