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by simonh
1749 days ago
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I'm not saying churn is a bad thing per se, I'm saying it renders any naive usage of the S&P as a proxy for company returns introduces a huge dollop of survivorship bias. You're adding up all the increased returns of the companies that did well and culling out any influence on the stats from companies that did sufficiently poorly, which is about half of the companies. |
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Survivorship introduces bias relative to the performance of the average company, but not to the performance of the average shareholder's portfolio. The largest ETFs have been S&P 500 ETFs since 2013; the index is the best readily available proxy for average investor returns.