A Dow Jones market data analysis, reported by the Wall Street Journal on October 28, 2026, finds that ten companies account for roughly two-thirds of S&P 500 third-quarter profit growth, with Micron and Nvidia alone contributing about a third. Excluding those ten, earnings growth falls from about 30% to about 10%. Professional investors say the concentration is not a critical threat to the rally, but it ties the market to the same bet on AI paying off.