Some fun facts:The five largest stocks now account for 22...

Some fun facts:
The five largest stocks now account for 22 percent of the S&P 500’s market cap. That bumper performance from Alphabet, Amazon, Apple, Facebook and Microsoft — which all set new highs this month — has led to a record degree of market concentration, according to a new research note from Goldman Sachs full of eye-catching numbers.

Said five stocks account for 15 percent of the S&P 500’s total earnings.

This concentration makes the market “vulnerable to an idiosyncratic shock,” Goldman’s analysts write. If the top five stocks were to fall by 10 percent, the bottom 100 of the S&P would need to rise by 90 percent just to keep the index flat.

• What could produce 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 C.E.O.s 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.”

FWIW