The NBBO for an average active stock is non-positive (locked or crossed) 10.58% and 4.05% of the time on, respectively, the NASDAQ and the NYSE inter-markets. Locks and crosses are frequent fleeting events that usually accompany significant price changes. Non-positive NBBOs arise because of (i)...

We document trade price clustering in the futures markets. We find clustering at prices of x.00 and x.50 for S&P 500 futures contracts. While trade price clustering is evident throughout time to maturity of these contracts, there is a dramatic change when the S&P 500 futures contract is...

This study directly compares the level and return predictability of short selling for NYSE stocks to a matched sample of Nasdaq stocks. When considering trading that executes on all exchanges, we document that the Nasdaq has greater levels of short selling, relative to total trading activity,...

"Using short-sale transactions data, we examine the relation between short selling and the weekend effect. We do not find that short selling is more abundant on Monday than on Friday, even for stocks that have higher Friday returns. We find that short sellers execute more short-sale volume...

We examine clustering of transaction prices in a sample that contains high-frequency trading firms’ transactions. We separate our sample into four categories: transactions with a high-frequency trading firm on both sides of the transaction, on only one side of the transaction (either liquidity...

We examine the impact of market maker concentration on adverse-selection costs for NASDAQ stocks and find that more market makers results in lower costs. Furthermore, this reduction in adverse selection exceeds the overall reduction in spreads that is attributable to market maker competition. We...