Assessing Measures of Toxic Order Flow and Early Warning Signals for Market Turbulence

Following the ``flash crash'' on May 6, 2010, warning signals for impending market stress have been in high demand, yet only the VPIN metric of Easley, Lopez de Prado and O'Hara (ELO) has claimed success. In addition, ELO find the metric useful in predicting short-term volatility. VPIN involves decomposing volume into active buys and sells. We utilize quotes and trade data to construct an accurate trade classification measure for E-mini S&P 500 futures. Against this benchmark, the ELO Bulk Volume Classification (BVC) scheme is inferior to a standard tick rule. Moreover, VPIN predicts volatility solely because increasing volatility induces systematic classification errors in the BVC procedure. We conclude that VPIN is unsuitable for capturing order flow toxicity or signaling ensuing market turbulence.