Social trading platforms vs. mutual funds: herding tendencies and portfolio risks*

This paper compares herding behavior between mutual funds and social trading platforms, where retail investors manage others' money, and examines its implications for risk co-movements. Utilizing unique social trading data alongside mutual fund data, we find that social trading portfolio managers exhibit less herding than mutual fund managers according to a transaction-based herding measure. However, a market-based herding measure reveals no significant difference in herding behavior, highlighting a limitation in the robustness of the transaction-based approach. We discuss factors influencing herding behavior in the social trading environment, suggesting higher overconfidence in social trading as a key factor. From an investor perspective, herding behavior can align portfolios, increasing the likelihood of common crisis events. Although we do not find a statistically significant relationship between the degree of herding and the likelihood of joint crisis events, our findings indicate that social trading portfolios have a 5.63 percentage point lower likelihood of joint crisis events compared to mutual funds.