Contract size changes in the options market: effects on market efficiency and investor behaviour

We study options market participants’ trading behaviour before and after the options multiplier increases. After the options multiplier increases, the options market becomes more efficient. By analysing the high-frequency microstructure dataset, we show that local retail and local institutional investors who trade in both options and futures markets trade more after the change in the multiplier. Our results imply that the increase in the market efficiency may be caused by fewer speculators. In addition, lottery stocks are traded more actively after the options multiplier increase.