Systematic trading behaviour and its informational effect: evidence from the OMXH

By using signed small trade turnover (SSTT) as a proxy of investors’ systematic trading behaviour and permanent price effect (PPE) as a proxy for informed trading, this article investigates the short-term outperformance of high SSTT stocks for categories of investors on the NASDAQ OMX Helsinki (OMXH) and whether the outperformance is best understood in the context of investor trading behaviour or informed trading. This study finds that the trading of high SSTT stocks is associated with a lower PPE than the trading of low SSTT stocks, which implies that the trading of high SSTT stocks is less informed than the trading of low SSTT stocks, and that the short-term outperformance of high SSTT stocks relative to low SSTT stocks is best explained within the behavioural finance framework, that is, by investors’ bias towards popular stocks proxied by SSTT, and not within the rational framework, that is, by informed trading proxied by the PPE. These findings are economically and statistically significant for all types of investors.