We describe a model for calculating the optimal quantity of debt and then apply it to the U.S. economy. The model consists of a large number of infinitely-lived households whose saving behavior is influenced by precautionary saving motives and borrowing constraints. This model incorporates a different role for government debt than the standard representative agent growth model and captures different trade-offs between the benefits and costs of varying its level. Government debt enhances the liquidity of households by providing additional assets for smoothing consumption (in addition to claims to capital) and effectively loosening borrowing constraints. By raising the interest rate, government debt makes assets less costly to hold and more effective in smoothing consumption. However, the implied taxes have wealth distribution, incentive, and insurance effects. Further, government debt crowds out capital (via higher interest rates) and lowers per capita consumption. Our quantitative analysis suggests that the crowding out effect is decisive for welfare. We also describe variations of the model which permit endogenous growth. It turns out that even with lump sum taxes and inelastic labor, government debt as well as government consumption have growth rate effects, thereby implying large welfare gains from reducing the level of debt.

Does macroeconomic volatility/uncertainty affect accumulation of net foreign assets? In OECD economies over the period 1970-2012, changes in country specific aggregate volatility are, after controlling for a wide array of factors, significantly positively associated with net foreign asset position. An increase in volatility (measured as the standard deviation of GDP growth) of 0.5% over period of 10 years is associated with an increase in the net foreign assets of around 8% of GDP. A standard open economy model with time varying aggregate uncertainty can quantitatively account for this relationship. The key mechanism is precautionary motive: more uncertainty induces residents to save more, and higher savings are in part channeled into foreign assets. We conclude that both data and theory suggest uncertainty/volatility is an important determinant of the medium/long run evolution of external imbalances in developed countries.

Between 2007 and 2013, U.S. households experienced a large and persistent decline in net worth. The objective of this paper is to study the business cycle implications of such a decline. We first develop a tractable monetary model in which households face idiosyncratic unemployment risk that they can partially self-insure using savings. A low level of liquid household wealth opens the door to self-fullfilling fluctuations: if wealth-poor households expect high unemployment, they have a strong precautionary incentive to cut spending, which can make the expectation of high unemployment a reality. Monetary policy, because of the zero lower bound, cannot rule out such expectations-driven recessions. In contrast, when wealth is sufficiently high, an aggressive monetary policy can keep the economy at full employment. Finally, we document that during the U.S. Great Recession wealth-poor households increased saving more sharply than richer households, pointing towards the importance of the precautionary channel over this period.