美联储过度储蓄的宏观经济效应

The Macroeconomic Effects of Excess Savings

Introduction Household wealth fluctuates significantly over the business cycle, with annual growth rates more volatile than nominal GDP in the U.S. post-war period. Excess savings, defined as wealth in excess of normal levels, contribute to smoothing consumption and differ substantially across households. The depletion of excess savings varies widely, masking significant heterogeneity. This study aims to quantify and characterize the depletion of excess savings and its macroeconomic implications, using data from the COVID-19 pandemic.

Background and Context During the pandemic, U.S. households drastically reduced spending and received large fiscal transfers, accumulating excess savings equivalent to about 10% of pre-crisis GDP. Concerns arose about potential rapid spending and inflation, highlighting the inadequacy of standard models in predicting the decumulation of excess savings. Two contrasting views exist: classical Keynesian economics suggests rapid decumulation due to high marginal propensities to consume (MPCs), while standard macroeconomic models with a representative agent predict no decumulation.

Model and Analysis The study uses a heterogeneous agent New Keynesian (HANK) model to analyze the mechanisms underlying the depletion of excess savings. Key findings include:

1. Distribution of Excess Savings: Households with less liquid wealth exhibit more Keynesian behavior, while those with more liquid wealth show more Ricardian behavior.
2. Partial Equilibrium Impulse Response: The response of aggregate consumption and saving is determined by the joint distribution of initial excess savings and micro iMPCs. iMPCs also amplify spending but are insufficient to fully characterize the response in general equilibrium.
3. Quantitative Model: A medium-scale HANK model is calibrated using insights from the analytical results. The model includes involuntary unemployment, union Nash bargaining, and asset revaluation effects, among others.
4. Simulation Results: The model simulates an accumulation period followed by a decumulation period. The accumulation period spans from the start of the pandemic to the third quarter of 2021, capturing the peak of excess savings. Post-peak, the model predicts a substantial but steadily waning boost to consumption, explaining up to 40% of the observed inflation surge in 2020 and 2021.

Conclusion The study provides a comprehensive framework for understanding the macroeconomic effects of excess savings, emphasizing the importance of heterogeneity in household behavior and the need for more sophisticated models to capture the complex interactions between savings, consumption, and inflation.