The Dow Jones Industrial Average and the S&P 500 index, the most popular stock-market gauges, usually move in lockstep. After all, they're both baskets of some of America's largest stocks, even though the Dow has just 30 and the S&P has 500 of them.
But in recent trading days, they have seen the lowest level of correlation since 2003, according to data from WSJ Market Data Group. A 15-year average of the Dow and the S&P 500 shows that the relationship is nearly perfect, at a correlation of 0.9557 on a scale from 0 to 1. However, the rolling 20-day period shows a reading of 0.4655. That's the lowest level of correlation between the S&P and the Dow industrials since August 4, 2003.
What's behind it? The recent tech slump has hit the S&P harder than the Dow, for one thing. And the financials, which are a huge part of the Dow, have been overperforming at the same time.