Crude oil and stocks are moving in lock step. Will it last? Crude-oil futures and the U.S. stock market are linked in a strange dance. Lately, oil has been moving nearly in lock step with equities. The correlation over the past month has been uncanny. In statistical terms, correlation is defined as the tendency of assets to move in the same direction over a given period. Perfect positive correlation, in which two securities move in complete lock step, is represented by the value 1. In perfect negative correlation, represented by negative 1, securities move in exactly opposite directions. A correlation of zero means price movements by the securities are completely random and independent of each other. Since late August, crude oil CLX5, +0.60% and the Dow Jones Industrial Average DJIA, -0.48% have been mostly positively correlated. As the chart below highlights, as oil (in red) has gone so have stock indexes like the Dow (in blue): FactSet Those moves intensified as turmoil in China markets reached a crescendo. According to Dow Jones data, since Aug. 19 this year oil has moved in the same direction as the Dow more than 72% of the time. Compared with 51.98% for all of 2014 and more than 57% in 2015, including Wednesday’s trade. The table below highlights that trend:YearDown days same directionUp days same directionTotal same directionTotal days% of days2014646713125251.982015614410518257.69Since Aug. 19117182572Aug. 19-Sept. 22, 201468142458.33Aug. 19-Sept. 22, 201377142458.33Source: Dow Jones datavia