Key Takeaways

  • Portfolios concentrated in few stocks expose investors to “FOMO risk” – the possibility of missing out on the small fraction (2.1%) of stocks responsible for nearly all global equity premium.
  • Contrary to the conventional belief that 30-40 stocks provide sufficient diversification, current market dynamics suggest that portfolios could require several hundred stocks for volatility and performance to converge to market levels.
  • Even small differences in annual returns caused by concentration accumulate significantly over time. A 1% annual return difference can lead to wealth outcomes diverging by roughly one-third over a 30-year horizon.

Watch the webinar recording here.

Summary

Motivation: Pension funds have shifted towards more concentrated equity portfolios, driven by ESG objectives, reputational concerns, and a desire for deeper corporate engagement. However, concentrated portfolios may carry material financial risks. The authors present new global evidence showing that traditional beliefs surrounding diversification benefits warrant reassessment, and introduce the concept of “FOMO risk”, the chance of missing the small number of stocks that generate most of the equity premium.

Methodology: The analysis draws on nearly 40 years of stock-level data, covering over 87,000 stocks across 47 developed and emerging markets from 1985 to 2023. The authors construct thousands of hypothetical portfolios of varying sizes to examine how portfolio concentration impacts volatility, returns, Sharpe ratios, and downside risks. They also incorporate ESG tilts and alternative weighting and selection methods to mirror realistic institutional investment approaches.

Findings:

  • Portfolios require substantially more than 30-40 stocks for full diversification, with volatility converging to market levels only at around 750 stocks.
  • Stock returns are extremely skewed: only 41% of stocks create positive wealth, while just 2.1% account for the entire global equity premium over the 40-year sample period. Concentrated portfolios thus have a high probability of missing the few stocks that drive long-term market performance.
  • Return dispersion is wide and declines only gradually as portfolio size increases: at 100 stocks, the gap between the 2.5th and the 97.5th percentile of returns is roughly 3.5% per year.
  • These persistent gaps translate into large performance differences over time. Even a 1% annual return difference compounds to materially different wealth outcomes over long horizons, with ending wealth levels diverging by roughly one-third after thirty years.
  • ESG-tilted portfolios exhibit similar diversification and FOMO risks, consistent with observations that ESG ratings are not meaningfully correlated with financial performance.
  • Portfolio optimization techniques – such as minimizing correlations or capping weights – can modestly “speed up” diversification, but they do not fully eliminate the risks inherent in concentration.
  • These results reflect a purely financial analysis; investors may still have legitimate non-financial reasons for holding more concentrated portfolios, such as ethical considerations or active engagement efforts.

Q&A Highlights:

  • Market concentration today: current concentration levels driven by the Magnificent 7 are unusually elevated, increasing FOMO risk; however, this risk persists throughout the full 40-year sample, as it is also driven by cross-sectional volatility.
  • No single “right” number of stocks: while empirical results suggest diversification requires far more than 30-40 stocks, the appropriate level of concentration ultimately depends on investor mandates and trade-offs and varies across geographies.
  • Active vs. passive investing: given only 2.1% of stocks drive all value creation, active managers must have strong conviction in their ability to consistently identify the narrow slice of value-creating stocks.
  • Portfolio construction and private assets: the framework can be applied to an investor’s specific investable universe, including private or less liquid assets, allowing funds to assess how concentration dynamics affect their portfolio risk and return.