This paper studies how random product innovations affect the time series properties of aggregates. It posits that recurring inventions of new intermediate goods differ in quality, and that their usage spreads gradually through the economy. It examines how fluctuations in per capita GNP are...

In a model with multiple Pareto-ranked equilibria we add trade in assets that pay based on the realization of a sunspot. Asset trading restricts the equilibrium set in a way that raises welfare by eliminating equilibria with a high likelihood of disasters. When the probability of a disaster is...

Cyclical patterns in earnings can arise when contracts between firms and their workers are incomplete, and when workers cannot borrow or lend so as to smooth their consumption. Effort cycles generate occasional large changes in earnings. These large changes are transitory, consistent with recent...

Investment of U.S. firms responds asymmetrically to Tobin's Q: investment of established firms -- 'intensive' investment -- reacts negatively to Q whereas investment of new firms -- 'extensive' investment -- responds positively and elastically to Q. This asymmetry, we argue, reflects a...

This paper extends Lucas (1978) to a production economy with two capital goods. It is an RBC model in which each unit of investment requires a new idea, an "option". When options are scarce, new capital is harder to put in place and the value of old capital rises. Thus the stock market and...

I estimate a model in which new technology entails random adjustment costs. Rapid adjustments may cause productivity slowdowns. These slowdowns last longer when retooling is costly. The model explains why growth-rate disasters are more likely than miracles, and why volatility of growth relates...

Was the Great Depression the outcome of a massive coordination failure? Or was it a unique equilibrium response to adverse shocks? More generally, do aggregates fluctuate partly because agents occasionally settle on inferior, low-level equilibria? These questions lie at the heart of the current...

The prospect of capital obsolescence inhibits investment. Investors thus become more optimistic when the obsolescence of their capital slows down. We propose a model with no fixed costs of investment, and random technological progress that induces obsolescence of capital in place. Spikes occur...

We study private equity in a dynamic general equilibrium model and ask two questions: (i) Why does the investment of venture funds respond more strongly to the business cycle than that of buyout funds? (ii) Why are venture funds returns higher than those of buyout? On (i), venture brings in new...