Are Index Funds Over-Diversified? | Summary and Q&A

June 22, 2019
Ben Felix
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Are Index Funds Over-Diversified?


Index funds do not lead to over diversification as they provide reliable and consistent outcomes for long-term investors.

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Key Insights

  • 🥺 Over diversification can lead to a wider range of outcomes, with a higher probability of negative outcomes relative to the market.
  • 🧡 Active share, which measures the difference between an investment strategy and the index, increases dispersion and the range of potential results.
  • 🛩️ Capturing risk premiums and achieving a reliable outcome requires broad diversification, as a small subset of stocks drives most of the market's returns.
  • 🥹 Holding all stocks in an index offers the surest way to avoid underperformance compared to actively managed portfolios with less diversification.
  • 🦡 Decreasing diversification decreases the likelihood of capturing risk premiums and increases the potential for a worse outcome.
  • 🫰 Index funds provide reliable outcomes for long-term investors who prioritize meeting their financial goals over trying to outperform the market.
  • ✳️ Diversification is essential for minimizing the risk of trailing the market and ensuring a more consistent outcome.


  • Every now, and then I hear the comment that index funds result in over diversification. The thinking goes that instead of buying all of the companies in an index, you might be able to focus on a smaller subset that you believe will perform better than the market as a whole. It makes sense. Of course you can't beat the market by holding it. The pr... Read More

Questions & Answers

Q: Why do some people argue that index funds can result in over diversification?

Some believe that by focusing on a smaller subset of companies that they believe will outperform the market, they can achieve better results than holding the entire index.

Q: How does active share affect the dispersion of outcomes?

Active share measures how different an investment strategy is from the index. As active share increases, the dispersion of outcomes also increases, leading to a wider range of potential results.

Q: Can a concentrated portfolio of dividend-paying stocks capture the value and profitability premiums?

While dividend growth stocks may have market-beating performance, this is primarily due to their exposure to factors such as value and profitability. Diversification, including both dividend-paying and non-paying stocks, allows for a more reliable outcome.

Q: How does diversification affect the reliability of outcomes?

The more diversified the portfolio, the more reliable the outcome becomes. Holding all the stocks in an index ensures that the investor captures the risk premiums and has a greater chance of achieving similar returns to the market.

Summary & Key Takeaways

  • Over diversification can lead to a wider range of outcomes, with a disproportionately large probability of negative outcomes.

  • Active share measures the extent of active management, and increasing active share leads to higher dispersion and a wider range of outcomes.

  • Diversification is crucial for capturing risk premiums and ensuring a reliable outcome in the market.

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