A number of delta-hedged equity option strategies exhibit very large average returns. We show that much of the profitability of these strategies can be explained by an IPCA factor model. The economic magnitude of the return-adjustment produced by IPCA is impressive: even before transaction costs, the average IPCA alpha of 46 long-short trading strategies constructed on previously discovered signals, is close to zero and contrasts with average realized returns of over 80 basis points per month. Our IPCA model can be used as a benchmark for assessing the performance of other option portfolios.

Although momentum exists in many markets throughout the world, explanations for momentum have largely been tested using US data. We investigate the extent to which US-based momentum explanations extend to the international context, using regression-based and portfolio approaches. Among the several hypotheses we consider, we find reliable support for the hypothesis that due to limited attention, investors underreact to information arriving in small bits rather than in large chunks, which results in momentum. We also find secondary support for the overconfidence hypothesis for momentum. Finally, we find that momentum is stronger in up-markets and less-volatile markets in the international context just as in the USA. This finding also accords with the investor overconfidence hypothesis, under the proviso that investors are more confident in rising, low-volatility markets.

Short sellers are widely known to be informed, which would typically suggest that they demand liquidity. We obtain comprehensive transaction-level data to decompose daily short volume into liquidity-demanding and liquidity-supplying components. Contrary to conventional wisdom, we show that the most informed short sellers are actually liquidity suppliers, not liquidity demanders. They are particularly informative about future returns on news days and trade on prominent cross-sectional return anomalies. Our analysis suggests that market making and opportunistic risk-bearing are unlikely to explain these findings. Instead, our results align with recent market microstructure theory, pointing to strategic liquidity provision by informed traders.

We document that implied volatility (IV) curves of short-term equity options frequently become concave prior to earnings announcements day (EAD), typically reflecting a bimodal risk-neutral distribution for the underlying stock price. Firms with concave IV curves exhibit significantly higher absolute stock returns on EAD and higher realized volatility after the announcement, rendering concavity an ex-ante signal for event risk. Returns on delta-neutral straddles, delta-neutral strangles, and delta- and vega-neutral calendar straddles are negative and significantly lower in the presence of concave IV curves, showing that investors pay a substantial premium to hedge against the gamma risk arising from this event.