Warnings that index funds have broken the stock market all imply a threshold: a share of the market at which price discovery fails. Nobody making the argument names it. Owen Lamont, writing in the Financial Analysts Journal, argues that no such number exists short of complete passive ownership, and that what actually determines whether prices stay informative is who is left doing the trading. His case, the strongest peer-reviewed research against it, and what the performance
The S&P 500's concentration in the Magnificent Seven has critics worried about indexing risk. But Hendrik Bessembinder's research reveals why index concentration actually strengthens the case for passive investing: just 4% of stocks drive all market returns, and active managers consistently miss these winners. Historical data shows market concentration has been normal for 150 years, from railroads to tech giants.
Robin Powell
Sep 9, 20258 min read
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