Effective Extension of Trading Hours

To uncover the complex feature of the effect of extending trading hours, I analyze what kind of the extension is effective on price efficiency and price stability, by utilizing an agent-based market model. Specifically, I examine whether the partial extension of trading hours—namely, implementing the pre-market session and the after-hours session—and what duration of the session is effective. The simulation result reveals that the implementation of both sessions could have a negative impact on price efficiency and stability if investors’ participation during the session is limited; it could result in more concentrated trading in the opening session, wider divergence between market prices and the fundamental value, and lower price stability. In addition, longer sessions are less beneficial (or more harmful). My result also shows that there are very few benefits to trade during the extended-hours sessions. Thus, my findings suggest that the extended-hours trading has a structural weakness which causes illiquidity during the session and lowers price efficiency and price stability during the regular-hour session. However, I find that the implementation of the pre-market session is far more beneficial than that of the after-hours session; exceptionally, the implementation of the short-term pre-market session could induce higher price efficiency and higher price stability regardless of the number of market participants during the session.