“In the boom years of the 1950s, the 10 biggest companies, including AT&T, DuPont, and General Motors, regularly exceeded 30% of the value of all U.S. stocks. In July 1955, GM alone—up 78% over the previous 12 months—amounted to 6.8% of the value of the entire U.S. stock market, according to the Center for Research in Security Prices.”
Read the full article at the Wall Street Journal.