We study the relationship between credit, stock trading and prices bubbles. The role of credit in financial bubbles is theoretically ambiguous. On the one hand, it may help rational arbitrageurs to trade against a bubble; on the other hand, it may enable naive speculators to buy overvalued assets. We construct a novel database containing every individual stock transaction in three major British companies during the 1720 South Sea Bubble. We link these transactions to daily margin loan positions and subscription lists of new share issues. We find that margin loan holders acted as extrapolators, i.e., they were more likely to buy (sell) following high (low) past returns. Loan holders also signed up to buy new shares of overvalued companies and incurred large trading losses. Our results suggest that credit provision was instrumental in fueling the bubble.
Would ambiguity averse investors hedge risk in equity markets?
(with Gleb Gertsman and Bas Werker)
This paper studies the conjecture that investors prefer derivative markets over the equity market when hedging risks. An investor who wants to hedge, say inflation or crash risk, generally faces substantially more beta uncertainty in the stock market than in the derivatives market. We show that an investor with smooth ambiguity aversion preferences avoids a hedge portfolio consisting of stocks, which is typically subject to large beta uncertainty. The ambiguity averse investor prefers to hedge using derivatives (TIPS and options) which are not subject to beta uncertainty. More specifically, we show that equilibrium risk premiums for assets with large beta uncertainty (long-short portfolio of stocks) decline once derivatives with less beta uncertainty (TIPS and options) are introduced. In line with this theory, we find that the inflation risk premium decreases significantly, in absolute terms, when TIPS are introduced.