PNU researcher investigates left-tail momentum in the Korean stock market

Left-tail risk (LT) stocks are those whose returns fall into the extreme end on the left side of the return distribution. In the hopes of mean-reverting to the normal price, investors usually hold on to these stocks. However, contrary to mean-reverting expectations, these stocks that have experienced extreme losses and high tail risks in the past tend to continue declining in the future, resulting in financial losses. This phenomenon, referred to as left-tail momentum (LTM), appears to challenge the traditional notion of a positive relationship between risk and return.

To investigate this market anomaly, a team of researchers, led by Prof. Eom from the School of Business at Pusan National University in South Korea, have recently re-verified the LTM phenomenon in the Korean stock markets through a cross-sectional comparison of all stocks by examining extreme risk situations. Their work was made available online on 10 February 2023 and published in Volume 87 of the International Review of Financial Analysis journal on 01 May 2023.

The researchers analyzed stock returns from July 2000 to June 2021 and standardized the distributions of these returns to cross-sectionally compare all stocks in the same criterion. By aligning the returns of all stocks within a predetermined threshold, they established a fair basis for comparing risks across different stocks. Their analysis revealed two types of LT stocks: those with fatter tails, reflecting higher tail risk and more frequent extreme losses, and those with thin tails, indicating relatively low tail risk and infrequent extreme losses.

The researchers then proceeded to investigate the LTM phenomenon within these groups by utilizing a measure called Value-at-Risk (VaR), which represents the boundary value associated with a specific probability in the distribution of stock returns. By utilizing VaR, they were able to assess the magnitude of potential financial losses, taking into consideration the tail-fatness property of the stock return distributions.

They found that the LTM phenomenon is not observed for all stocks that have experienced extreme losses in the past, but rather only for stocks with thin tails—stocks that have lower tail risk and have experienced extreme losses infrequently in the past. These results challenge previous assumptions, demonstrating that the LTM phenomenon does not contradict the conventional positive relationship between risk and return.

“If the fat tail property is viewed as a frequent occurrence of extreme losses, it can be interpreted as a high tail risk. Since LTM phenomenon was clearly observed only in stocks with a thin tail distribution, it is difficult to see it as evidence that violates the positive relationship between risk and return in traditional financial theory,” emphasize the researchers.

Overall, the research reveals that the LTM phenomenon is driven by investors overvaluing stocks with low left-tail risks compared to those with high left-tail risks. “This study looks forward to an interesting discourse in further studies investigating whether the LTM phenomenon that involves a low left-tail risk can be explained in terms of the risk–return trade-off relationship,” conclude the researchers.

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Reference

DOI: https://doi.org/10.1016/j.irfa.2023.102570

About the institute
Pusan National University, located in Busan, South Korea, was founded in 1946, and is now the no. 1 national university of South Korea in research and educational competency. The multi-campus university also has other smaller campuses in Yangsan, Miryang, and Ami. The university prides itself on the principles of truth, freedom, and service, and has approximately 30,000 students, 1200 professors, and 750 faculty members. The university is composed of 14 colleges (schools) and one independent division, with 103 departments in all.

Website: https://www.pusan.ac.kr/eng/Main.do

About the authors
Cheoljun Eom is a professor at the School of Business at Pusan National University in South Korea. He was a postdoctoral researcher at Pohang University of Science and Technology (POSTECH) from 1999–2000, and worked in Hyundai Investment and Security Co. Ltd. as a manager from 2001–2002, where he developed the total asset allocation system. His research interests include asset pricing, portfolio optimization, financial econometrics, and econophysics. He has published more than 90 papers in the field of Finance and Interdisciplinary Science. After winning an award of 2009 Best Researcher in Pusan National University, he has received a few research excellence awards, and recently won the Korea Financial Investment Association Outstanding Paper Award at the 2023 joint conference with the Allied Korea Finance Associations.

Google Scholar website: https://scholar.google.com/citations?user=zEVhXPEAAAAJ&hl=en

ORCID id: 0000-0001-6362-9947

Yunsung Eom is a professor at the School of Business at Hansung University in Seoul, South Korea. He graduated from the Department of Fine Arts and the Department of Business Administration at Seoul National University and also obtained his master's and doctoral degrees in Finance there. He has conducted research as a visiting scholar at the University of Washington and the Economic Research Institute, Bank of Korea. His research interests include behavioral finance, market microstructure, investments, and algorithmic trading. His most cited research is “The disposition effect and investment performance in the futures market,” which is published in the Journal of Futures Markets in 2009.

Google Scholar website: https://scholar.google.com/citations?hl=en&user=M443k0EAAAAJ

Jong Won Park has been a professor of Finance at the College of Business at the University of Seoul since 2005. Before joining UOS, Professor Park was an assistant and associate professor at the College of Business at Cheju National University. He obtained his Ph.D. in Finance from Seoul National University in March 1995. His research interests focus on empirical asset pricing, market volatility, capital markets and anomalies, derivatives/risk management, retirement and public pension, corporate finance, market regulation, and macro-finance.

Google Scholar website: https://scholar.google.com/citations?hl=en&user=6qUbCb0AAAAJ&view_op=list_works&sortby=pubdate