Person:

Greenwood, Robin

We present an extrapolative model of bubbles. In the model, many investors form their demand for a risky asset by weighing two signals: an average of the asset’s past price changes and the asset’s degree of overvaluation. The two signals are in conflict, and investors “waver” over time in the relative weight they put on them. The model predicts that good news about fundamentals can trigger large price bubbles. We analyze the patterns of cash-flow news that generate the largest bubbles, the reasons why bubbles collapse, and the frequency with which they occur. The model also predicts that bubbles will be accompanied by high trading volume and that volume increases with past asset returns. We present empirical evidence that bears on some of the model’s distinctive predictions.

We develop a model in which capital moves quickly within an asset class but slowly between asset classes. While most investors specialize in a single asset class, a handful of generalists can gradually reallocate capital across markets. Upon the arrival of a large supply shock, prices of risk in the directly impacted asset class become disconnected from those in others. Over the long run, capital flows between markets and prices of risk become more closely aligned. While prices in the directly impacted market initially overreact to the supply shock, we show that prices in related asset classes underreact under plausible conditions. We use the model to assess event-study evidence on the impact of recent large-scale asset purchases by central banks.

Using historical data on post-war financial crises around the world, we show that crises are substantially predictable. The combination of rapid credit and asset price growth over the prior three years, whether in the nonfinancial business or the household sector, is associated with about a 40% probability of entering a financial crisis within the next three years. This compares with a roughly 7% probability in normal times, when neither credit nor asset price growth has been elevated. Our evidence cuts against the view that financial crises are unpredictable “bolts from the sky” and points toward the Kindleberger-Minsky view that crises are the byproduct of predictable, boom-bust credit cycles. The predictability we document favors macro-financial policies that “lean against the wind” of credit market booms. Replication kit and appendix available here: https://www.hbs.edu/faculty/Pages/item.aspx?num=60191

We study the stock market effects of the arrival of the three rounds of “stimulus checks” to U.S. taxpayers and the single round of direct payments to Hong Kong citizens. The first two rounds of U.S. checks appear to have increased retail buying and share prices of retail-dominated portfolios. The Hong Kong payments increased overall turnover and share prices on the Hong Kong Stock Exchange. We cannot rule out that these price effects were permanent. The findings raise novel questions about the role of fiscal stimulus in the stock market. (Authors have furnished an Internet Appendix, which is available on the Oxford University Press Web site next to the link to the final published paper online.)