The problem of classifying trades as buys or sells is examined. I propose estimated quotes for midpoint and bid/ask tests and a modeling approach to classification. Prevailing quotes are estimated using flexible approximations to the distribution for delays of quotes relative to trade...

We develop a price maker/taker model to study how a financial transaction tax affects markets. We find taxes widen quoted and effective spreads by more than twice the tax. Taxes increase volatility slightly (without intermediation) to significantly (with intermediation). High taxes may halve...