Eur. Phys. J. B 61, 241-246 (2008)
https://doi.org/10.1140/epjb/e2008-00050-0

Increasing market efficiency in the stock markets

¹ Department of Physics, Korea University, Seoul, 136-701, Korea
² Division of Social Sciences, International Christian University, Osawa, Mitaka, Tokyo, 181-8585, Japan
³ School of Physics, Korea Institute for Advanced Study, Seoul, 130-722, Korea

Corresponding author: ^a imkim@korea.ac.kr

Received: 31 January 2007
Revised: 13 December 2007
Published online: 6 February 2008

Abstract

We study the temporal evolutions of three stock markets; Standard and Poor's 500 index, Nikkei 225 Stock Average, and the Korea Composite Stock Price Index. We observe that the probability density function of the log-return has a fat tail but the tail index has been increasing continuously in recent years. We have also found that the variance of the autocorrelation function, the scaling exponent of the standard deviation, and the statistical complexity decrease, but that the entropy density increases as time goes over time. We introduce a modified microscopic spin model and simulate the model to confirm such increasing and decreasing tendencies in statistical quantities. These findings indicate that these three stock markets are becoming more efficient.