Crowdedness denotes a scenario in which investors collectively and simultaneously acquire significant volumes of the same assets. The behavior might signal collective wisdom by sophisticated fundamental and quant investors, or it could be driven by macroeconomic or market news.
On the other hand, it could be driven by irrational investor behavior (which can lead to bubbles). An important question for investors is what happens when too much money flows into the same stocks and/or strategies? A team of BlackRock researchers tackled this important question in the Spring 2025 issue of The Journal of Beta Investment Strategies. Their study, A Demand-Based Equity Risk Factor: Crowdedness, offers fresh insights into how crowded trades can systematically impact stock returns and portfolio performance.
The Research Focus: Measuring What Can’t Be Seen
The authors examined a deceptively simple yet profound concept: crowdedness in equity markets. Unlike traditional risk factors that focus on company fundamentals or market characteristics, crowdedness represents a demand-side phenomenon—it’s about who’s buying what, and how much.
The research team set out to answer several key questions:
- How can we quantify crowdedness in equity markets?
- Does crowdedness behave like a systematic risk factor that affects stock returns?
- Can investors use crowdedness measures to improve portfolio construction and risk management?
Using data extracted from 13F reports of US institutional investors, the authors formulated a novel demand-based equity risk factor to measure crowdedness. This enabled them to analyze institutional holdings, trading patterns, and market flows and determine the impact of the crowdedness factor. They categorized investors based on three fundamental fund characteristics:
- Equity assets under management to assess the scale of investors, distinguishing between large and small institutions.
- Active share, determined by the average absolute difference between an investor’s holding weights and the theoretical market weights derived from market capitalization (though free-float, which adjusts for closely held shares, is typically used). This distinguishes between active and passive investors.
- Turnover, which compares an investor’s holding weights with those of the previous quarter, gauges the extent of their market trading activity.
The authors then classified institutional investors as “large, passive, and low” if they exhibited larger equity AUM, lower active share, and lower turnover values compared with the median of all investors. They define crowdedness as the percentage of holdings attributed to investors who focus on smaller, active, higher turnover strategies that contribute to crowding in the stocks. This group consisted of four categories of investors:
- Institutional investors with smaller equity AUM, larger active share, or greater turnover than the median.
- Very small institutional investors who do not meet the $100 million threshold requirement for filing Form 13F.
- Households, which are not mandated to report their holdings and, therefore, are covered by the factor.
- Foreign investors without branches in the United States, who are not bound by this policy, hence their holdings are accounted for in the crowdedness construction. Therefore, stocks predominantly held by those investors are considered “crowded.”
The authors then assessed crowdedness as a unique risk factor within BlackRock’s Fundamental Risk Equity US Model, which encompasses a market factor, 50 industry factors, and 12 style factors. Their data sample covered the period from 2014 through September 2023. The following is a summary of their key findings.
Key Findings
1) Crowdedness as a Systematic Risk Factor
Crowdedness is a unique factor demonstrating minimal correlation with established factors. In addition, it’s a statistically significant, systematic risk factor that affects stock returns across different time periods and market conditions—stocks with high crowdedness measures showed distinct return patterns compared with less crowded securities.
2) The Demand-Supply Imbalance Effect
When many investors crowd into similar positions, it creates demand that can push prices away from fundamental values—creating vulnerabilities that can lead to sharp reversals when the crowd begins to exit. Sorting 2,000 US stocks into quintiles, they found stocks with pronounced crowding exposures demonstrated notably negative returns, high volatility, negative maximum drawdowns, and positive skewness.
3) Cross-Sectional Predictability
Crowdedness measures helped predict which stocks might underperform in the future. This predictive power was particularly strong during periods of market stress when crowded positions became unstable.
4) Factor Interaction Effects
Crowdedness doesn’t operate in isolation. It interacts with other well-known risk factors, sometimes amplifying their effects and other times tempering them, suggesting that traditional factor models might be incomplete without considering crowdedness.
5) Factor Returns
The crowdedness factor exhibited a negative 1.1% annualized return with minimal risk, resulting in a significant information ratio of negative 0.91.
Key Takeaways for Investors
For Institutional Investors
Large institutions need to be particularly mindful of crowdedness because their size can both contribute to and be affected by crowded trades.
For Quantitative Strategies
The paper suggests that:
- Factor-based strategies may become less effective as they become more crowded.
- Incorporating crowdedness measures into factor models could improve risk-adjusted returns.
- Diversification across less crowded factors might provide better long-term performance.
The Broader Market Context
The paper’s findings are particularly relevant in today’s market environment, where:
- ETFs and index funds can concentrate flows into similar securities.
- Social media and algorithmic trading can amplify crowding effects.
- Market concentration in large-cap stocks has increased.
Too Crowded for Comfort
The research by BlackRock represents an important step forward in understanding modern market dynamics. As markets become increasingly interconnected and algorithmic, the concept of crowdedness will likely become more relevant for investors and risk managers.
Bottom line: In the investment party, it’s not just about finding the right room—it’s about knowing when that room is getting too crowded for comfort.
Larry Swedroe is the author or co-author of 18 books on investing, including his latest, Enrich Your Future. He is also a consultant to RIAs as an educator on investment strategies.
