ABSTRACT We argue that short sellers affect prices in a significant and systematic manner. In particular, we contend that speculative short sales contribute to the weekend effect: The inability to trade over the weekend is likely to cause these short sellers to close their speculative positions on Fridays and reestablish new short positions on Mondays causing stock prices to rise on Fridays and fall on Mondays. We find evidence in support of this hypothesis based on a comparison of high short‐interest stocks and low short‐interest stocks, stocks with and without actively traded options, IPOs, zero short‐interest stocks, and highly volatile stocks.

We investigate the relationship between IPO long-run underperformance (Ritter, 1991; Loughran and Ritter, 1995) and the idiosyncratic risk puzzle (Ang, Hodrick, Xing, and Zhang, 2006) or the phenomenon of abnormally low returns for stocks with high idiosyncratic risk. We find that IPO long-run underperformance is a manifestation of surprisingly low returns for high idiosyncratic risk stocks. IPO underperformance disappears after we control for idiosyncratic risk. On the other hand, we find that the idiosyncratic risk puzzle is magnified by IPO underperformance. Our results are robust to various specifications or sample requirements. We evaluate a couple of potential common causes for the two puzzles and conclude that investors’ preferences for stocks with lottery features is the primary mechanism linking the two puzzles.