The Uncertainty Trap: Effectiveness of macroeconomic policy

バブル崩壊後のわが国では、度重なる財政出動、金融緩和によっても持続的な経済成長が生まれず、「失われた30年」という表現が定着した。2008年のリーマンショック後の米国においても、「長期停滞論」が有力となった。こうした経験は伝統的な財政/金融政策の有効性に疑問符をつけるものであった。

マクロ経済政策の有効性を損なう要因として「不確実性」が注目されている。本論文では、この問題につき理論的な考察を行う。スタンダードなミクロ的基礎づけを持つマクロ経済理論の問題点を整理した上で、それに代わる統計物理学的な方法を説明する。このモデルを用いて、不確実性の高まりが財政金融政策に代表されるマクロ経済政策の有効性を低下させることを示す。

In this paper, we explore the effectiveness of macroeconomic policy. To achieve this goal, we first discuss the theoretical framework of macroeconomics in Section 2. We explain why the standard microeconomic foundations of macroeconomics are mistaken and argue that Keynesian economics or what Tobin (1993) called the Old Keynesian view, according to which real aggregate demand determines aggregate production, can best explain the actual macroeconomy. We then briefly explain the microeconomic foundation of Keynes’ principle of effective demand based on methods used in statistical physics in Section 3. Using this model, we explore the effectiveness of macroeconomic policy in Section 4. In the model, the difference between micro demand shocks and macro demand shocks is significant. Individual micro demand shocks cannot be observed. In fact, only the aggregate fluctuations caused by such unobservable micro shocks are observed. This is analogous to the observation of thermal fluctuations governed by temperature in physics. By contrast, macro demand shocks are observable in various forms, one of which is macroeconomic policy such as fiscal/monetary policy. We demonstrate that macroeconomic policy becomes ineffective with very low levels of aggregate demand. This result holds true irrespective of macroeconomic model specifics and is generic. Section 5 provides concluding remarks.