유동성함정하에서 준칙 대 재량

This paper aims to compare and analyze the properties of rules versus discretion using a theoretical model in which liquidity traps can occur and policy authorities retain control over fiscal policy as well as monetary one. As in Keynes (1936), the source of a liquidity trap is an aggregate demand shock. In this paper we analyze the properties of discretionary solution according to three scenarios: the economy is not liquidity trapped, liquidity trapped only in the bad state, and liquidity trapped in both states. We find that the possibility of a liquidity trap has three main results. First, as in the certainty model in which there is no liquidity trap, rules are always better than discretionary policies. This means that rules solution achieves the optimal rational expectations solution, as a second best. Second, when the economy is liquidity trapped, discretionary policy can have a deflationary bias, unlike the standard analysis conducted in the absence of a liquidity trap. Eggertsson (2006) and Dhami and al-Nowaihi (2011b) also derive the same result. In particular, Eggertsson (2006) refers the inefficiency of a solution under discretion entirely to the deflationary bias. The result of this paper, however, differs from that of Eggertsson (2006) in that a discretionary solution does not always create the deflationary bias. Accordingly, the inefficiency of discretionary policy is not utterly stemmed from a deflationary bias. Finally, another property of a solution under discretion is that a higher value of desired output relative to the natural rate may either increase or decrease the level of social welfare depending upon the parameter values of the model. This upshot is in a marked contrast to that of Dhami and al-Nowaihi (2011b) who propose that a higher value of desired output raises the level of social welfare by boosting output and employment.