We test the hypothesis that arbitrageurs amplify economic shocks in equity markets. The ability of speculators to hold short positions depends on asset values. Shorts are often reduced following good news about a stock. Therefore, the prices of highly shorted stocks are excessively sensitive to shocks compared with stocks with little short interest. We confirm this hypothesis using several empirical strategies including two quasi-experiments. In particular, we establish that the price of highly shorted stocks overshoots after good earnings news due to short covering compared with other stocks.

Using data on the political contributions and stock holdings of U.S. investment managers, we find that mutual fund managers who make campaign donations to Democrats hold less of their portfolios (relative to non-donors or Republican donors) in companies that are deemed socially irresponsible (e.g., tobacco, guns, or defense firms or companies with bad employee relations or diversity records). Although explicit socially responsible investing (SRI) funds are more likely to be managed by Democratic managers, this result holds for non-SRI funds and after controlling for other fund and manager characteristics. The effect is more than one-half of the underweighting observed for SRI funds.

Economists have traditionally viewed futures prices as fully informative about future economic activity and asset prices. We argue that open interest could be more informative than futures prices in the presence of hedging demand and limited risk absorption capacity in futures markets. We find that movements in open interest are highly pro-cyclical, correlated with both macroeconomic activity and movements in asset prices. Movements in commodity market interest predict commodity returns, bond returns, and movements in the short rate even after controlling for other known predictors. To a lesser degree, movements in open interest predict returns in currency, bond, and stock markets.