Tick Size Wars: The Market Quality Effects of Pricing Grid Competition

We explore the effects of a "tick size war" in which European trading venues directly competed on the minimum pricing increment in the limit order book, the tick size. We find that venues that reduced their tick size immediately captured market shares of both quoted and executed volume from the exchanges that kept their ticks large. We find that tick size competition improves market quality, reducing trading costs, and increasing market-wide depth and volume. These market quality improvements are strongest in stocks where the bid-ask spread was constrained to one tick, where liquidity providers use the finer pricing grid to engage in price competition.