We examine some basic data on the evolution of aggregate short interest, both during the dot-com era, and at other times in history. Total short interest moves in a countercyclical fashion. For example, short interest in NASDAQ stocks actually declines as the NASDAQ index approaches its peak. Moreover, this decline does not seem to reflect a substitution away from outright short-selling and towards put options, as the ratio of put-to-call volume displays the same countercyclical tendency. The evidence suggests that: i) arbitrageurs are reluctant to bet against aggregate mispricings; and ii) short-selling does not play a particularly helpful role in stabilizing the overall stock market.

We propose that stock‐market participation is influenced by social interaction. In our model, any given “social” investor finds the market more attractive when more of his peers participate. We test this theory using data from the Health and Retirement Study, and find that social households—those who interact with their neighbors, or attend church—are substantially more likely to invest in the market than non‐social households, controlling for wealth, race, education, and risk tolerance. Moreover, consistent with a peer‐effects story, the impact of sociability is stronger in states where stock‐market participation rates are higher.