The five largest stocks in the S&P 500 now account for 22 percent of the index’s market capitalization, according to Goldman Sachs. The soaring share prices of Alphabet, Amazon, Apple, Facebook and Microsoft — which all set new highs this month — has led to this record degree of market concentration, which makes some analysts nervous, notes the DealBook newsletter.
So far this year, the top five stocks are up 35 percent collectively. The index’s other 495 companies are down 5 percent. The top five stocks trade at a valuation of 31 times next year’s estimated earnings. The rest of the index trades at 18 times. If the top five stocks were to fall by 10 percent, the bottom 100 of the blue-chip club would need to rise by 90 percent just to keep the index flat.
This makes the market “vulnerable to an idiosyncratic shock,” Goldman’s analysts wrote. What could produce such a shock? The analysts note that the dot-com boom ended around the time that the U.S. government won a big antitrust case against Microsoft in 2000. On Monday, the chief executives of Alphabet, Amazon, Apple and Facebook will testify before Congress as part of an investigation into “the dominance of a small number of digital platforms and the adequacy of existing antitrust laws and enforcement.”