Momentum Profits and Idiosyncratic Volatility: The Korean Evidence

Purpose – This study focuses on the profitability of momentum trading in the Korean stock market. More specifically, an examination of the relationship between momentum returns and idiosyncratic volatility (IVol) is conducted to determine whether momentum profits can be explained by IVol. Design/Methodology/Approach – We form portfolios based on their past performance and examine the momentum, or contrarian returns, as the difference between winning and losing portfolios. To confirm that the momentum strategy provides excess returns, we study the relationship between momentum returns and IVol. We also examine the Fama and French (1993) three-factor model to see whether systematic risk affects momentum profits. We control firm size, stock price, and turnover to determine robustness. Finally, we investigate a time-series relationship between aggregate IVol and momentum profits. Findings – We illustrate that excess returns are obtained from a momentum strategy, not a contrarian strategy, in the Korean stock market. Momentum returns are higher among high IVol stocks, especially high IVol winners. Examining the Fama and French (1993) three-factor model, we find that momentum returns cannot be explained by systematic risk. The findings are robust after controlling for factors such as firm size, book-to-market ratio, and turnover. We confirm the effect of IVol on momentum returns by illustrating that a time-series relationship between momentum returns and aggregate IVol is positive. Originality/Value – This paper is among the first, to our knowledge, to examine the relationship between momentum profits and IVol in the Korean stock market, one of the mature financial markets. The findings in this study can be applied to better understand the sources of gains from the momentum strategy in international stock markets.