Noise traders, excess volatility, and a securities transactions tax

Abstract

Proponents of a securities transactions tax have suggested that such a tax may reduce stock return volatility. The argument is that, to the extent that short-term speculative trading volume is the source of excess volatility, a tax that reduces such volume will reduce volatility. In the context of a simple general equilibrium model, it is shown that this partial equilibrium argument is misleading and in large part incorrect. In the absence of a tax, the model generates equilibria in which the risky asset's price exhibits excess volatility and agents engage in excess trading activity owing to the presence of destabilizing noise traders. Within the context of the model, it is shown that, although a transactions tax can reduce the volatility of the risky asset's price, the reduction in price volatility is accompanied by a fall in the asset's price as agents discount the future tax liability associated with risky asset ownership. Consequently, although price volatility may decrease slightly, the fall in equilibrium prices more than compensates, and the volatiltiy of risky asset returns unambiguously increases with the level of the transactions tax.