Shares of everything from manufacturers to banks to oil-production companies are rebounding together after tumbling in unison earlier this month, a phenomenon that could lead to more turbulence ahead.
Correlations among the S&P 500’s 11 sectors, a measure of how different stock groups move in relation to one another, spiked as the index suffered its first correction in two years last week and further increased when stocks began bouncing back from those lows. They recently hit the highest level since the U.S. presidential election in 2016, according to a Goldman Sachs analysis.
https://www.wsj.com/articles/stocks-are-moving-in-tandem-that-can-be-scary-1518720399
