「無知之幕」後的貨幣政策

Abstract

本文藉由模型分析以探討中央銀行面對「無知之幕」時，對貨幣政策的選擇問題，意即在模型中，政策制定者僅能獲得與消費行為和生產力衝擊相關之資訊，而無從得知消費者的效用函數。關於在此限制下政策制定者的偏好，本文提出與之相應的價值函數以供政策評估，並將其應用於比較價格平抑(Price Stability)、產出平抑(Output Stability) 和通貨膨脹目標制(Inflation Targeting) 三政策在新凱因斯(New Keynesian) 模型中之均衡結果。在我們的評估標準下，價格平抑和產出平抑會在不同參數條件下物有優劣，因為政策制定者在缺乏效用函數資訊下無法精確計算出產出缺口。即便如此，在考量到對現實世界的參數估計後，我們發現在數值模擬得出的最適政策中，價格平抑仍遠較產出平抑為重要。

We analyze the problem of the choice of a central bank constitution. We model the decision problem as a choice behind a veil of ignorance in which the policy maker only receives information about predicted behavior of agents under different policies. We derive a policy criterion that only relies on this information and is robust to misspecification of the utilitarian welfare function. We compare price stabilization, output stabilization, and inflation targeting in a standard new Keynesian model with Calvo price staggering. Under our policy criterion, the policy maker perceives a tradeoff between output stabilization and price stabilization. The reason is that in the absence of knowledge about a utilitarian welfare function, stabilizing the natural level of output is not normatively desirable. Despite these findings, we show that for numerical approximations of parameters the utilitarian results of the standard new Keynesian model are suprisingly robust — the optimal policy under our criterion places a strong emphasis on price stability.