Effective Spread

Effective spread differs from quoted spread by capturing the actual slippage incurred by traders relative to the market mid-point at execution, rather than the static bid-ask spread shown on the order book. For a buy order executed at price P against a mid-quote M, the effective spread equals 2 * (P - M). This metric is fundamental to market microstructure analysis and insider-trading detection platforms, as it quantifies the true transaction cost and reveals whether execution occurred within or outside the spread, indicating potential information leakage or market impact.

In insider-trading surveillance, elevated effective spreads on insider transactions may indicate information-motivated trading or attempts to minimize market impact through algorithmic execution. Conversely, trades executing significantly inside the spread could signal front-running or layering behavior. Monitoring the distribution of effective spreads across PDMR and beneficial owner transactions provides a quantitative signal for the cluster-signal and sigma-score modules, enabling detection of abnormal execution patterns correlated with material nonpublic information events.