S&P 500 Stability Masks Weakness Across U.S. Stocks, Economist Says

新火集团 chief economist 付鹏 says large companies are keeping the S&P 500 steady while most U.S. stocks retreat, a split he warns could leave markets vulnerable to a rapid rise in volatility.

His assessment centers on a sharp gap between the index’s largest companies and the wider market. He says passive investment flows and investors concentrating in large stocks have helped support the index even as most other shares have experienced deeper technical pullbacks.

The S&P 500 weights companies by market capitalization, giving its largest members the greatest influence over its level. Their strength can keep the index steady while declines spread among smaller members. An earlier look at S&P 500 market breadth examined how the index can gain while many of its stocks lag.

付鹏 says market breadth, a measure of how widely stocks participate in a market move, is nearing a critical point. He warns that volatility could rise quickly if that point is reached.