The Friedman rule states that steady-state welfare is maximized when there is deflation at the real rate of interest. Recent work by Khan et al (2003) uses a richer model but still finds deflation optimal. In an otherwise standard new Keynesian model we show that, if households have hyperbolic discounting, small positive rates of inflation can be optimal. In our baseline calibration, the optimal rate of inflation is 2.1% and remains positive across a wide range of calibrations.

Most DSGE models assume full information and model-consistent expectations. This paper relaxes both these assumptions in the context of the stochastic growth model with incomplete markets and heterogeneous agents. Households do not have direct knowledge of the structure of economy or the values of aggregate quanti?ties; instead they form expectations by learning from the prices in their market-consistent information sets. The economy converges quickly to an equilibrium which is similar to the equilibrium with model-consistent expectations and market-consistent information. Learning does not introduce strong dynamics at the aggre-gate level, though more interesting things happen at the household level. At least in the context of this model, assumptions about information seem important for aggregates; assumptions about the ability to form model-consistent expectations less so.

Information is "market-consistent" if agents only use market prices to infer the underlying states of the economy. This paper applies this concept to a stochastic growth model with incomplete markets and heterogeneous agents. The economy with market-consistent information can never replicate the full information equilibrium, and there are substantial differences in impulse responses to aggregate productivity shocks. These results are robust to the introduction of a noisy public signal and aggregate financial markets. We argue that the principle of market-consistent information should be applied to any model with incomplete markets.

The paper sets out a theory of hedonic adaptation and resilience. By distinguishing between stocks and flows of psychological resources, it suggests a new way to think about the dynamics of human well-being or ‘happiness’. Central to the analysis is a concept we refer to as hedonic capital. We build on the idea that the evolutionary function of happiness is as a motivating device. Our model successfully replicates the patterns routinely found in well-being data – particularly the empirical regularity of an approximately stable level of well-being and the adaptive tendency to return towards that level. The formal model provides a number of testable empirical predictions.

Rational expectations solutions are usually derived by assuming that all state variables relevant to forward-looking behaviour are directly observable, or that they are “…an invertible function of observables” (Mehra and Prescott, 1980). Using a framework that nests linearised DSGE models, we give a number of results useful for the analysis of linear rational expectations models with restricted information sets. We distinguish between instantaneous and asymptotic invertibility, and show that the latter may require significantly less information than the former. We also show that non-invertibility of the information set can have significant implications for the time series properties of economies.

This paper suggests a way to think about human well-being and psychological health. It distinguishes between mental stocks and flows. Central to thenanalysis is a concept we refer to as hedonic capital. This can be thought of as a level of emotional coping resources, or as the underlying stock to which the economist’s idea of a flow of utility corresponds. The model replicates the patterns found in the recent empirical psychology and economics literature: there is an approximately stable level of mental well-being and an automatic tendency to adapt back towards that level. Conventional economic theory does not fit these facts.

Nearly all post-war recessions were preceded by oil-price shocks, but is this because spikes in the price of oil cause economic downturns? At the heart of this question lies an identification problem: oil prices and the state of the world economy are endogenously determined. This paper uses terrorist incidents as an instrumental variable. In an international panel of industries, we show that, after correction for simultaneity bias -- though not before -- the price of oil has large negative effects upon profitability. We test for weak instruments and check sub-sample robustness. Our findings seem to lend support to the claim that oil-price spikes can be a source of recessions.

Using a standard dynamic general equilibrium model, we show that the interaction of staggered nominal contracts with hyperbolic discounting leads to inflation having significant long-run effects on real variables.

Nearly all post-war recessions have been preceded by oil-price shocks, but is this because spikes in the price of petroleum cause economic downturns? Most research has ignored an identification problem: oil prices and the state of the world economy are endogenously determined. This paper uses terrorist incidents as an instrumental variable. In an international panel of industries, we show that after correction for simultaneity bias — though not before — the price of oil has large negative effects upon profitability. Our results seem to lend support to the claim that oil-price spikes can be a source of recessions.

We provide a microfounded account of imperfect information in the stochastic growth model which dramatically changes the properties of the model. We describe heterogenous households that acquire information about aggregates through their participation in markets. If markets are incomplete, household information will be imperfect. We solve the model taking account of the infinite regress of expectations that this lack of information implies. We derive analytical and numerical results to show that imperfect information can significantly change the properties of the model: under virtually all calibrations the impact response of consumption to a positive aggregate technology shock is negative.

How is the impact of monetary policy affected by the nature of nominal debt contracts? How does this change if the interest payments on the debt are fixed or floating? To address these questions, we add a model of financial institutions' behaviour to a dynamic general equilibrium model in which some households face credit constraints. We analyse these affects of inflationary shocks, and derive implications for monetary policy. We question the common view that inflationary shocks necessarily result in debtors increasing their consumption. We also provide a potential explanation for interest rate smoothing on the part of central banks.

We relax the assumption of full information that underlies most dynamic general equilibrium models, and instead assume agents optimally form estimates of the states from an incomplete information set. We derive a version of the Kalman filter that is endogenous to agents' optimising decisions, and state conditions for its convergence. We show the (restrictive) conditions under which the endogenous Kalman filter will at least asymptotically reveal the true states. In general we show that incomplete information can have significant implications for the time-series properties of economies. We provide a Matlab toolkit which allows the easy implementation of models with incomplete information.

Models with habit formation in consumption have proved useful in understanding a number of macroeconomic features. The key finding of this paper is that, when households can use their labor supply to smooth consumption, habit formation worsens a dynamic model’s response to both monetary and technology shocks. Some of the counterfactual implications of a model with habit formation can be rectified by introducing credit constrained households.

This paper proposes a new way to think about happiness. It distinguishes between stocks and flows. Central to the analysis is a concept we call 'hedonic capital'. The paper sets out a model of the dynamics of wellbeing in which bad life-shocks are smoothed by the drawing down of hedonic capital. The model fits the patterns found in the empirical literature: the existence of a stable level of wellbeing and a tendency to return gradually towards that level. It offers a theory of hedonic adaptation.

We provide a simple model of sticky nominal debt contracts and fixed rate debt that can easily be embedded in a dynamic general equilibrium framework. Once linearized, the debt process increases the order of autoregressive dynamics in the system by one; thus potentially introducing more complex adjustment processes.

In this paper, we develop an explanation for why events in one market may trigger similar events in other markets, even though at first sight the markets appear to be only weakly related. We allow for escape dynamics in each market, and show that an escape in one market is contagious because it more than doubles the probability of a similar escape in another market. We claim that contagion is strong since escapes become highly synchronised across markets. Spillovers are weak because the instantaneous spillover of events from one market to another is small. To illustrate our result, we demonstrate how a currency crisis may be contagious with only weak links between countries. Other examples where weak spillovers would create strong contagion are various models of monetary policy, imperfect competition and endogenous growth.