Adverse Selection Indicator

The Adverse Selection Indicator isolates the informational risk component within market spreads by decomposing the effective spread into three components: order processing costs, inventory costs, and adverse selection costs. In insider-trading surveillance and quant scoring contexts, elevated adverse selection signals suggest that informed trading activity is concentrated in a security, manifesting as larger half-spreads on buy orders relative to sell orders, or vice versa. This asymmetry typically reflects market makers' rational pricing adjustment when they face counterparties with superior information about fundamental value.

In quantitative insider-trading detection frameworks, adverse selection indicators are calibrated to flag securities where order flow toxicity correlates with subsequent price movements, particularly around PDMR transactions, Form 4 filings, or material nonpublic information leakage windows. The indicator is sensitive to order flow direction predictability, transaction size concentration, and temporal clustering of informed trading. Cross-sectional ranking of adverse selection across a universe improves alpha generation by identifying securities where information asymmetry premia are mispriced or where insider activity is creating detectable microstructure distortions.