Edouard Challe

Episodes of low natural interest rates, even transitory, pose a challenge to monetary policy, by possibly causing the effective lower bound (ELB) on the policy rate to bind. Those episodes are more likely to occur not only when the natural rate is low on average but also when fluctuations around its average level are large. We study the responsiveness of the natural interest rate to structural aggregate shocks affecting the aggregate supply of and demand for savings. Using a quantitative overlapping-generations model, we trace back this responsiveness to the slopes of aggregate savings supply and demand curves and argue that both curves have likely flattened over the past four decades in the US This implies a greater sensitivity of the natural interest rate to structural shocks affecting the supply of and demand for aggregate savings – making it more likely, all else equal, that it fall into negative territory.

We study optimal monetary policy in an analytically tractable heterogeneous agent New Keynesian model with rich cross-sectional heterogeneity. Optimal policy differs from a representative agent benchmark because monetary policy can affect consumption inequality, by stabilizing consumption risk arising from both idiosyncratic shocks and unequal exposures to aggregate shocks. The trade-off between consumption inequality, productive efficiency, and price stability is summarized in a simple linear-quadratic problem yielding interpretable target criteria. Stabilizing consumption inequality requires putting some weight on stabilizing the level of output, and correspondingly reducing the weights on the output gap and price level relative to the representative agent benchmark.

I study optimal monetary policy in a sticky-price economy wherein households precautionary-save against uninsured, endogenous unemployment risk. In this economy greater unemployment risk raises desired savings, causing aggregate demand to fall and feed back to greater unemployment risk. This deflationary spiral is constrained inefficient and calls for an accommodative monetary policy response: after a contractionary aggregate shock the policy rate should be kept significantly lower and for longer than in the perfect-insurance benchmark. For example, the usual prescription obtained under perfect insurance of a hike in the policy rate in the face of a bad supply (i.e., productivity or cost-push) shock is easily overturned. The optimal policy breaks the deflationary spiral and takes the dynamics of the imperfect-insurance economy close to that of the perfect-insurance benchmark. These results are derived in an economy with zero asset supply (zero liquidity) and are thus independent of any redistributive effect of monetary policy on household wealth.

We construct, and then estimate by maximum likelihood, a tractable dynamic stochastic general equilibrium model with incomplete insurance and heterogenous agents. The key feature of our framework is that cross‐sectional heterogeneity remains finite dimensional. The solution to the model thus admits a state‐space representation that can be used to recover the distribution of the model’s parameters. Household heterogeneity expands the set of observables to cross‐sectional moments available at the business‐cycle frequency (in addition to the usual macro and monetary time series). Incomplete insurance gives rise to a precautionary motive for holding wealth that propagates aggregate shocks via (i) a stabilizing aggregate supply effect, working through the supply of capital, and (ii) a destabilizing aggregate demand effect coming from the feedback loop between unemployment risk and precautionary saving. Using the estimated model to measure the contribution of precautionary savings to the propagation of recent recessions, we find strong aggregate demand effects during the Great Recession and, to a lesser extent, during the 1990–1991 recession. In contrast, the supply effect at least offsets the demand effect during the 2001 recession.

We study the macroeconomic implications of time-varying precautionary savings within a general equilibrium model with borrowing constraints, aggregate shocks and uninsurable idiosyncratic unemployment risk. Our framework generates limited cross-sectional household heterogeneity as an equilibrium outcome, thereby making it possible to analyse the role of precautionary saving over the business cycle in an analytically tractable way. The time-series behaviour of aggregate consumption generated by our model is closer to the data than that implied by the hand-to-mouth and representative-agent models, and it is comparable to that produced by the Krusell and Smith (1998) model.

We analyse the term structure of interest rates in a general equilibrium model with incomplete markets, borrowing constraint, and positive net supply of government bonds. Uninsured idiosyncratic shocks generate bond trades, while aggregate shocks cause fluctuations in the trading price of bonds. Long bonds command a “liquidation risk premium” over short bonds, because they may have to be liquidated before maturity – following a bad idiosyncratic shock – precisely when their resale value is low – due to the simultaneous occurrence of a bad aggregate shock. Our framework endogenously generates limited cross-sectional wealth heterogeneity among the agents (despite the presence of uninsured idiosyncratic shocks), which allows us to characterise analytically the shape of the entire yield curve, including the yields on bonds of arbitrarily long maturities. Agentsʼ desire to hedge the idiosyncratic risk together with their fear of having to liquidate long bonds at unfavourable terms implies that a greater bond supply raises the level of the yield curve, while an increase in the relative supply of long bonds raises its slope.

We analyse the term structure of interest rates in a general equilibrium model with incomplete markets, borrowing constraint, and positive net supply of government bonds. Uninsured idiosyncratic shocks generate bond trades, while aggregate shocks cause fluctuations in the trading price of bonds. Long bonds command a “liquidation risk premium” over short bonds, because they may have to be liquidated before maturity – following a bad idiosyncratic shock – precisely when their resale value is low – due to the simultaneous occurrence of a bad aggregate shock. Our framework endogenously generates limited cross-sectional wealth heterogeneity among the agents (despite the presence of uninsured idiosyncratic shocks), which allows us to characterise analytically the shape of the entire yield curve, including the yields on bonds of arbitrarily long maturities. Agentsʼ desire to hedge the idiosyncratic risk together with their fear of having to liquidate long bonds at unfavourable terms implies that a greater bond supply raises the level of the yield curve, while an increase in the relative supply of long bonds raises its slope.

We analyse the risk-taking behaviour of heterogenous intermediaries that are protected by limited liability and choose both their amount of leverage and the risk exposure of their portfolio. Due to the opacity of the financial sector, outside providers of funds cannot distinguish“prudent” intermediaries from those“imprudent” ones that voluntarily hold high-risk portfolios and expose themselves to the risk of bankrupcy. We show how the number of imprudent intermediaries is determined in equilibrium jointly with the interest rate, and how both ultimately depend on the cross-sectional distribution of intermediaries’capital. One implication of our analysis is that an exogenous increase in the supply of funds to the intermediary sector lowers interest rates and raises the number of imprudent intermediaries. Another one is that easy financing may lead an increasing number of intermediaries to gamble for resurection following a bad shock to the sector ‘scapital, again raising economywide systemic risk.

Financial crises are often associated with an endogenous credit reversal followed by a fall in asset prices and serious disruptions in the financial sector. To account for this sequence of events, this paper constructs a model where excessive risk-taking by investors leads to a bubble in asset prices, and where the supply of credit to these investors is endogenous. We show that the interplay between excessive risk-taking and the endogeneity of credit may give rise to multiple equilibria associated with different levels of lending, asset prices, and output. Stochastic equilibria lead, with positive probability, to an inefficient liquidity dry-up, a market crash, and widespread failures by borrowers. The possibility of multiple equilibria and self-fulfilling crises is shown to be related to the severity of the risk-shifting problem in the economy.