Market concentration: How big a worry

S&P 500 returns this year have been nothing short of spectacular, with the index rising an eye-popping 26% ytd. This stellar performance owes to a handful of technology stocks-the Magnificent 7-which returned 41% ytd and accounted for an astonishing 47% of the index's gains. Just how anomalous US equity market concentration is today, and how worried investors should be about it, is Top of Mind.