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.

We use information from over 2 million trading strategies randomly generated using real data and from strategies that survive the publication process to infer the statistical properties of the set of strategies that could have been studied by researchers. Using this set, we compute t-statistic thresholds that control for multiple hypothesis testing, when searching for anomalies, at 3.8 and 3.4 for time-series and cross-sectional regressions, respectively. We estimate the expected proportion of false rejections that researchers would produce if they failed to account for multiple hypothesis testing to be about 45%.