标题： 股票市场中的持续集体趋势 显示英文标题

标题： Persistent collective trend in stock markets

摘要： 对股票指数上升和下降期间股票价格的集体趋势存在显著差异提供了实证证据。 研究了1991年至2008年间道琼斯工业平均指数及其股票成分的数据。 计算了股票之间的皮尔逊类型相关性，并对股票对和时间进行平均。 结果表明存在一种普遍趋势：当股票指数下跌时，股票价格的变化比股票指数上涨时更加相关。 对数据的详细统计分析表明，观察到的差异是显著的，这表明投资者中存在一种持续的恐惧因素。 显示英文摘要

摘要： Empirical evidence is given for a significant difference in the collective trend of the share prices during the stock index rising and falling periods. Data on the Dow Jones Industrial Average and its stock components are studied between 1991 and 2008. Pearson-type correlations are computed between the stocks and averaged over stock-pairs and time. The results indicate a general trend: whenever the stock index is falling the stock prices are changing in a more correlated manner than in case the stock index is ascending. A thorough statistical analysis of the data shows that the observed difference is significant, suggesting a constant-fear factor among stockholders.