2014年-IMF国际货币组织全球_Liquidity_Trap_and_Excessive_Leverage_49页_419kb

Summary of "Liquidity Trap and Excessive Leverage" by Anton Korinek and Alp Simsek

Core Content

This paper explores the role of macroprudential policies in addressing liquidity traps caused by excessive leverage and deleveraging. It presents a Keynesian model to analyze how borrowers' and lenders' behavior during a liquidity trap affects aggregate demand and economic efficiency. The study highlights the importance of ex-ante interventions in debt markets to prevent inefficiencies that arise from demand externalities and underinsurance.

Main Viewpoints

1. Liquidity Trap and Deleveraging

• A liquidity trap occurs when interest rates are constrained by the zero lower bound, preventing the economy from stimulating aggregate demand effectively.
• Deleveraging by constrained agents (borrowers) leads to a reduction in aggregate demand, which can push the economy into a liquidity trap.
• Borrowers with a stronger motive to borrow (e.g., due to impatience) can cause the economy to fall into a liquidity trap, even though the interest rate is at its lower bound.

2. Aggregate Demand Externalities

• Ex-ante leverage decisions by borrowers create aggregate demand externalities because they affect lenders' income and overall output.
• These externalities lead to a constrained inefficient equilibrium, where the competitive equilibrium does not maximize social welfare.
• MPC (Marginal Propensity to Consume) differences between borrowers and lenders determine the magnitude of inefficiency:
  • Borrowers have a higher MPC than lenders, so they spend more from liquid wealth, reducing aggregate demand and output.
  • This leads to a deeper recession and greater inefficiency.

3. Macroprudential Policies as a Solution

• Ex-ante macroprudential policies such as debt limits and mandatory insurance requirements can improve welfare by reducing excessive leverage.
• These policies are more effective than monetary policy in addressing excessive leverage, as monetary policy may inadvertently increase leverage.
• Mandatory insurance can help mitigate the negative effects of deleveraging by transferring liquid wealth to borrowers, who have a higher MPC, thus increasing aggregate demand.

4. Uncertainty and Underinsurance

• Uncertainty about future financial shocks leads to underinsurance of borrowers.
• Mandatory insurance requirements can help reduce underinsurance, leading to better outcomes for all agents.
• This result supports the idea of indexing mortgage liabilities to house prices, as proposed by Shiller and Weiss (1999).

5. Preventive Monetary Policies

• Contractionary monetary policies (e.g., raising interest rates) may not be effective in addressing aggregate demand externalities.
• In fact, raising interest rates during the leverage accumulation phase can increase leverage by creating a temporary recession and transferring wealth from borrowers to lenders.
• Raising the inflation target is a preventive monetary policy that can help reduce the incidence of liquidity traps.

Key Findings

• Excessive leverage is a key driver of liquidity traps and demand-driven recessions.
• Macroprudential policies are more effective than monetary policy in mitigating these effects.
• Aggregate demand externalities are distinct from pecuniary externalities and are more severe in a liquidity trap.
• Fire-sale externalities can exacerbate aggregate demand externalities, leading to more severe recessions.
• Anticipated deleveraging leads to suboptimal ex-ante decisions due to ignoring general equilibrium effects.

Implications for Policy

• Ex-ante debt regulation (e.g., debt limits) and mandatory insurance can improve economic outcomes during liquidity traps.
• Monetary policy should be supplemented with macroprudential measures to address leverage-related inefficiencies.
• Inflation targeting can be a useful tool to prevent liquidity traps and reduce the need for large interventions.

Model Structure

• The model assumes a simple Keynesian framework with two types of households: borrowers and lenders.
• Households are symmetric except for their discount factors (borrowers have a lower discount factor).
• A borrowing constraint is introduced in period 1, leading to deleveraging and a liquidity trap.
• Real interest rates are bounded from below, and the lower bound is exogenous.
• Equilibrium is defined by the interaction of consumption, savings, and labor supply with market clearing conditions.

Empirical Relevance

• The paper is grounded in empirical observations of household leverage and interest rates in the US.
• Figure 1 shows the rise in household debt before 2008 and the subsequent deleveraging.
• Figure 2 illustrates the constrained real interest rates in the US post-2008, supporting the liquidity trap hypothesis.

Conclusion

The paper argues that ex-ante macroprudential policies are necessary to address inefficiencies caused by excessive leverage and deleveraging in a liquidity trap. It shows that monetary policy is less effective and can even worsen the situation, while insurance requirements and debt limits offer more promising solutions. The model also provides insights into the interaction between aggregate demand externalities and fire-sale externalities, suggesting that deleveraging episodes involving asset fire-sales are particularly damaging to the economy.