06 Jan 2021 Ariel Investment's Mellody Hobson and John Rogers: What worked over the past decade is unlikely to work over the next ( Portfolio )

...when six companies account for nearly 25% of the index and 77% of its gains over the 12 months through September, this high-octane growth-stock cluster isn’t your grandfather’s Oldsmobile. Investors in this crowded trade simply aren’t as diversified as they think.