Decimal Trading and Market Impact

Abstract

Using high-frequency data and a carefully constructed 1-1 matched sample of control (non decimal) stocks, we isolate the effects of decimalization for a sample of NYSE-listed common stocks trading in decimals. We find that decimalization has resulted in significantly lower quoted and effective bid/ask spreads and that the most popular quoted spread is 1 cent. The available depths at the best bid and ask prices are also significantly lower. Together, these spread-depth results deliver a mixed verdict on market liquidity after decimalization. We find that decimalization has resulted in significant increases (decreases) in relatively smaller size (larger size) trades and trading volume. The frequency of quote updates and autoquotes in decimal stocks following decimalization has also increased significantly. Regional stock exchanges also appear to be significantly more active in competing for order flow. Our results have important research and policy implications.