Liquidity beyond the inside spread: measuring and using information in the limit order book

World equity markets increasingly convert to electronic trading, in many cases adopting the format of a pure electronic order book without intermediaries. A distinguishing feature of this format is that a high proportion of available liquidity is committed (displayed) rather than implicit or hidden. We examine the properties of a measure of liquidity, the Cost of Round Trip trade (CRT), which aggregates the status of the limit order book at any moment in time for a specific transaction size. CRT, which measures the ex ante committed liquidity immediately available in the market, complements the effective spread, which measures the ex post combination of the committed and hidden liquidity available over a period of time. We use data from the Toronto Stock Exchange to compare CRT to the quoted and effective spreads, and estimate its ability to predict the subsequent trading activity. While we propose CRT as a research tool, we also advocate its use by exchanges to indicate to investors the level of committed liquidity.