The Better-Than-Average Effect in Investing

The better-than-average effect, also called the above-average effect, is a cognitive bias in which most people rate themselves as better than the median in a given domain. In surveys of drivers, 88% report that they are above-average drivers; in surveys of managers, 80% believe they are among the top 20% of managers. The effect is logically impossible (by definition, no more than half the population can be above the median) yet persists across cultures and across skill levels. In investing and trading, the better-than-average effect is particularly destructive. Surveys consistently show that 70–90% of individual investors believe they can beat the market or possess above-average stock-picking skill. Yet empirical data demonstrates that fewer than 20% of active fund managers beat a low-cost index fund, and fewer than 1% of retail traders do so. The persistent gap between subjective self-assessment and objective evidence suggests that the better-than-average effect is a universal feature of how investors think about themselves.

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The better-than-average effect in investing is the widespread belief among individual traders and investors that their skill, knowledge, and returns exceed those of their peers and the market average. Most investors survey themselves as above-median performers, yet objective data shows the median investor underperforms index funds by 2–4% annually after costs. This gap between subjective confidence (most people believe they are above average) and objective reality (most people underperform) is the better-than-average effect. The bias drives excessive trading, insufficient diversification, and concentration in high-conviction positions. It also creates emotional hardship: the average investor has convinced themselves that they are above-average, so when their returns lag the market, they must rationalize the underperformance as bad luck or unfair market conditions rather than lack of skill. Understanding the better-than-average effect and its prevalence is essential to building realistic expectations and avoiding the costs of overconfidence.

Quick definition: The better-than-average effect is a cognitive bias in which most people rate themselves as better than the median in a given domain, even though this is statistically impossible for more than half the population to be true.

Key Takeaways

• Surveys show that 80–90% of investors believe they are above-average performers, yet fewer than 20% actually beat low-cost index funds after costs.
• The better-than-average effect is logically impossible; by definition, only 50% of people can be above-average, yet self-assessments typically place 70–80% above average.
• The effect is driven by positive illusions, selective memory, and the difficulty of assessing one's true performance in an ambiguous domain like trading.
• The bias leads to excessive trading, underutilization of index funds, and concentration in high-conviction positions—all of which drag on returns.
• Accepting that you are likely near-average (at best) and building a diversified, low-cost portfolio is a rational response to the prevalence of the better-than-average effect.

The Mathematical Impossibility and the Empirical Reality

The better-than-average effect is one of the few psychological biases with a mathematical impossibility at its core. If you ask a large population to rate whether they are above, at, or below average in a specific domain, the average self-rating should equal 50% (since half the population, by definition, is below average and half is above). Yet in study after study, the average self-rating is 60–70%, and in some samples it is as high as 80–90%.

In investing, the effect is stark. A 2019 survey by Vanguard found that 73% of individual investors rate their investment performance as above-average compared to peers. Yet the same survey found that the median individual investor's portfolio underperformed a simple 60/40 index portfolio by 1.6% per year. The gap is enormous: if 73% of investors are above-average, the average investor's portfolio should outperform 50% of peers. Instead, the median portfolio underperforms more than 80% of passive strategies.

Another data point: The SPIVA scorecard (from S&P Dow Jones Indices) tracks the percentage of active mutual fund managers who beat their benchmarks. Over a 15-year period, only 8% of large-cap fund managers beat the S&P 500 index after fees. Yet surveys show that 70–80% of fund managers believe they can beat their benchmarks. The gap between belief and reality is 70 percentage points or more.

Real-world example: A survey of retail day traders found that 95% of respondents believed they could consistently outperform the market or generate above-average returns. Yet empirical data on trading accounts shows that fewer than 1% of day traders are profitable after transaction costs. The better-than-average effect reached its maximum: nearly everyone believed they were above-average, yet nearly everyone was below-average.

Why the Better-Than-Average Effect Persists

Several mechanisms allow the better-than-average effect to persist despite overwhelming empirical evidence against it.

The first is selective attention and memory. You remember your winning trades vividly and in detail. You may forget your losing trades or remember them hazily. When asked "Have you beaten the market this year?", the vivid memory of your two biggest winners dominates your answer, even if you actually underperformed the market as a whole.

The second mechanism is anchoring on a flawed reference group. You may compare yourself to your friends, family, or coworkers rather than to the true population of investors. Your friends probably discuss their successful trades more than their failures; thus your perceived comparison group is biased upward. Compared to this biased peer group, you appear above-average.

The third mechanism is asymmetric attribution. You attribute your successes to your own skill and intelligence but attribute your failures to external factors (bad luck, market conditions, broker execution, timing). This asymmetry inflates your self-assessment. A trader might think: "I beat the market because I am skilled at picking stocks. When I underperform, it is because the market is irrational." This narrative preserves the belief that they are above-average.

The fourth mechanism is the illusion of unique insight. You believe you have special information, analysis, or perspective that others lack. A trader might feel they understand a company's growth prospects better than the market, or that they have identified a technical pattern others have missed. This sense of unique insight makes them feel above-average. Yet unique insight is rare; most traders have access to the same public information and perform similar analyses. The uniqueness is usually an illusion.

A fifth mechanism is difficulty of assessment. Unlike driving (where you directly observe your own behavior and can count accidents), investing is ambiguous. Your performance is partly skill, partly luck, partly regime-dependent (style bias), and partly outcome of your amount of risk-taking. It is nearly impossible to disentangle these factors in real time. This ambiguity leaves room for positive illusions. A trader can convince themselves they are skilled without any real evidence.

The Better-Than-Average Effect Across Skill Levels

Interestingly, the better-than-average effect is not confined to novices. Even experienced investors and professional traders exhibit the effect. A study of professional investors found that 80% of them expected to outperform the market over the next five years, despite the fact that historical outperformance rates for their asset class were below 20%. The effect is not about stupidity or ignorance; it is a systematic feature of how humans assess themselves.

However, the effect is stronger among those with lower actual competence. A trader who has underperformed the market for five years will still often believe they possess skill and will still self-rate as above-average. But the magnitude of the self-rating gap is larger for weak performers than for strong performers. This suggests that the worse you actually perform, the larger your positive illusion about your performance needs to be.

Real-world data supports this: A study tracked individual investor performance and their own confidence ratings. Those investors who underperformed most severely were the most likely to maintain high confidence in their future performance. The relationship was inverse: the worse your actual returns, the higher your confidence. This is almost the opposite of rational updating.

The Better-Than-Average Effect and Diversification

The better-than-average effect leads to insufficient diversification and excessive concentration. A trader who believes they are above-average is more likely to hold a concentrated portfolio of their best ideas. A portfolio with 10 high-conviction picks (each representing 10% of assets) feels more appropriate to someone who believes they are above-average at picking stocks. A diversified portfolio of 50 stocks or an index fund feels like "giving up" or "admitting they are average."

Yet the data is clear: concentrated portfolios underperform diversified portfolios after adjusting for volatility, particularly when the concentration is driven by the better-than-average effect rather than by genuine alpha. A trader holding 10 favorite stocks, each of which they believe will outperform, is probably wrong about at least 5 of them. If those 5 underperform by 10% while the 5 winners outperform by 10%, the portfolio shows zero outperformance yet took on significant idiosyncratic risk.

The Cost of the Better-Than-Average Effect

The better-than-average effect is expensive. It leads to:

1. Excessive trading. Traders who believe they are above-average are more likely to believe they can identify mispricings and exploit them through frequent trading. Transaction costs and taxes drain 1–3% annually.

2. Inadequate diversification. Concentrated portfolios underperform diversified ones by 1–2% annually after adjusting for risk.

3. Insufficient index fund allocation. Many above-average-believing investors avoid index funds, missing out on the low-cost, tax-efficient core they should hold. This might cost 0.5–1% annually.

4. Emotional pain from underperformance. An investor who believes they are above-average and then faces years of underperformance experiences psychological distress and must rationalize the gap between expectation and reality. This often leads to doubling down rather than accepting the evidence.

5. Opportunity cost. An investor who spends five hours per week analyzing stocks and managing their portfolio could have spent that time on higher-value activities (career development, business building, etc.). The opportunity cost is easily 0.5–1% annually in foregone income or productivity.

The total cost of the better-than-average effect for the average retail investor is probably 3–5% per year in reduced risk-adjusted returns.

The Stable Delusion: Why the Effect Persists

One of the most interesting features of the better-than-average effect is its stability over time. People are exposed to years of feedback (their returns) that ought to correct their self-assessment, yet they do not update much. A trader underperforms the market for five years straight, yet maintains the belief that they are above-average.

This stability arises partly from the rationalization mechanisms described above (attribution of failures to external factors, selective memory of successes). But it also arises from the simple fact that correcting a long-held belief about yourself is psychologically difficult. Your self-image as a skilled investor is part of your identity. Updating that belief downward requires admitting that you were wrong for years, that your time spent on analysis was wasted, and that your special insight was actually illusion. These admissions are painful and most people avoid them by maintaining the positive illusion.

Better-Than-Average vs. Confidence Intervals

The better-than-average effect is related to but distinct from the overconfidence effect. The overconfidence effect is the tendency to hold too-narrow confidence intervals around forecasts (a 90% confidence interval contains the true value only 50% of the time). The better-than-average effect is the tendency to rate yourself as above-average in skill, knowledge, and performance.

A trader might exhibit both effects: they might have narrow confidence intervals around their forecast of next year's market return (overconfidence effect) and also believe they are above-average at picking stocks (better-than-average effect). The two biases are distinct but often co-occur.

The Role of Comparison Difficulty

The better-than-average effect is weakest in domains where comparison is easy and feedback is clear. In chess, tennis, or golf, there are objective rankings and leaderboards. Most people do not believe they are above-average chess players because they can play a computer and see immediately that they lose. But in investing, comparison is difficult. Most individual investors do not know what the market return was last year (though they could easily look it up), let alone know how their portfolio performed relative to a benchmark.

If every investor received a detailed report each year showing their actual returns versus a market-tracking benchmark and a breakdown of their returns into skill and luck components, the better-than-average effect might be weaker. But most investors receive no such feedback, so the better-than-average illusion persists.

Summary

The better-than-average effect is a cognitive bias in which most people rate themselves as better than the median in a domain, despite the statistical impossibility of this being true. In investing, surveys show that 70–90% of investors believe they are above-average, yet empirical data shows that fewer than 20% of active managers and fewer than 1% of retail traders beat index funds after costs. The effect is driven by selective attention, asymmetric attribution, illusion of unique insight, and the difficulty of objectively assessing investment performance. The effect leads to excessive trading, insufficient diversification, and concentration in high-conviction positions—all of which reduce returns. Interestingly, the worse an investor's actual performance, the more likely they are to maintain high confidence in their future performance, suggesting the better-than-average effect serves as a psychological defense against painful evidence of underperformance. Accepting that you are likely near-average (at best) and building a diversified, low-cost portfolio aligned with your actual capabilities is the rational response.

Real-World Examples

The SPIVA data on active managers. The S&P Dow Jones Indices' SPIVA scorecard shows that over 15-year periods, only 8–15% of active equity fund managers beat their benchmarks. Yet surveys of fund managers show that 70–80% believe they can beat their benchmarks. The gap between belief and reality is 55–70 percentage points—a massive effect.

Retail traders' self-perception vs. reality. Surveys of retail day traders show that 90–95% believe they can beat the market or generate consistent returns. Yet empirical analysis of trading account data shows that fewer than 1% of day traders achieve positive net returns after commissions and spreads. The gap is nearly 95 percentage points.

Investor self-assessment surveys. A 2022 Vanguard survey found that 65% of investors rated their portfolio performance as above-average relative to peers. Yet when the researchers actually calculated the median investor's portfolio return versus a simple benchmark, the median investor underperformed by 1.6% per year. The subjective self-assessment and the objective performance diverged sharply.

The gambler's fallacy and positive illusions. A trader holds a stock that has fallen 30% from their purchase price. Most traders still believe it is a good investment (better-than-average belief in their original analysis). They do not sell; they hold or add to the position. Later, many traders still do not sell even if the stock goes down another 30%. The better-than-average effect keeps them holding, convinced that their original thesis was right and the market is temporarily irrational.

Common Mistakes

1. Comparing yourself to your friend group instead of the market. Your friends probably discuss their successful trades more than their failures. When you compare yourself to this biased peer group, you appear above-average. But your peer group is not representative of the universe of traders.

2. Measuring performance over short periods. A trader measures their return over one quarter or one year and finds they beat the market. Over that short period, luck dominates skill. They believe they are above-average based on short-term performance. Over longer periods (five or ten years), their underperformance would be clear.

3. Attributing all wins to skill and all losses to external factors. A trader's winning trade is due to their analytical skill; a losing trade is due to bad luck or market manipulation. This asymmetric attribution preserves the belief in above-average competence.

4. Not tracking performance against a clear benchmark. Many investors do not know what their portfolio returned last year relative to a 60/40 stock-bond index. Without this clarity, it is easy to maintain the illusion of above-average performance.

5. Underestimating the costs of active trading. A trader might earn 8% gross returns before costs and believe they are above-average, yet pay 2% in fees and transaction costs, netting 6% (below the market return of 7%). The costs of active management drag most traders below-average performance.

FAQ

If I actually can beat the market, how would I know?

Track your risk-adjusted returns versus a benchmark for at least five years. If you consistently beat the benchmark (say, by 2% or more per year) net of all costs, fees, and taxes, you might have genuine edge. But ensure you are comparing apples to apples: a small-cap value portfolio should be compared to a small-cap value benchmark, not to the S&P 500. Also account for the luck component: 20 years of data is more convincing than five years, because randomness averages out.

Is the better-than-average effect stronger for beginners or experienced investors?

The effect is present in both, but the magnitude of the gap between belief and reality is larger for beginners. An experienced investor who has underperformed for 10 years might still believe they are above-average, but the illusion is less extreme than a beginner who has never tracked performance. However, both populations are more likely to be above-average in their own minds than in reality.

Can the better-than-average effect ever be motivating or beneficial?

In some contexts, a bit of positive illusion might help people attempt difficult things (starting a business, learning a new skill). But in financial markets, the better-than-average effect is reliably costly. The costs of the illusion (excessive trading, inadequate diversification, emotional pain from underperformance) exceed any psychological benefits.

How does the better-than-average effect relate to overconfidence?

The better-than-average effect is a specific form of overconfidence bias. Overconfidence is the broader tendency to overestimate your abilities and knowledge. The better-than-average effect is the specific belief that you are better than the median. Both biases lead to excessive risk-taking and poor financial outcomes.

What percentage of investors should actually be above-average?

By definition, exactly 50% of investors can be above-average. But if we narrow the definition to "beating the market after costs," the number is much lower, probably 10–20% (mostly lucky rather than skilled). If we narrow it further to "beating the market by 2%+ per year net of all costs due to actual edge," the number is probably below 1%.

Does accepting that you are average mean you should give up on investing skill?

No. It means you should accept that beating the market is very difficult and rare, and that chasing it through active trading and stock picking is likely to be costly. But you can still pursue legitimate edge in specific areas (arbitrage, market making, factor investing with evidence-based strategies, etc.). The key is to be realistic about the probability of success and the effort required.

How can I overcome the better-than-average effect in myself?

Implement external accountability: publish your predictions and track your actual performance; compare your portfolio to a benchmark index monthly; work with a fee-only financial advisor who is not incentivized to make you feel above-average; read books on investment history and statistics that document the rarity of true alpha. Over time, evidence-based feedback can overcome the psychological need to believe you are above-average.

Related Concepts

• What Is Overconfidence Bias?
• The Dunning-Kruger Effect
• Overestimating Your Knowledge
• How Overconfidence Costs You in Trading
• Recency Bias Defined

Summary

The better-than-average effect is a cognitive bias in which most people rate themselves as better than the median, even though this is statistically impossible for more than half the population to be true. In investing, surveys show that 70–90% of investors believe they are above-average performers, yet empirical evidence shows that fewer than 20% of active managers and fewer than 1% of retail traders beat index funds after costs. The bias is driven by selective attention to successes, asymmetric attribution of wins to skill and losses to luck, illusion of unique insight, and the difficulty of objectively assessing investment performance. The effect leads to excessive trading, insufficient diversification, and concentration in high-conviction bets—all of which reduce returns by 3–5% per year. Accepting that you are likely near-average (at best) and building a diversified, low-cost portfolio is the rational response. Transparent performance tracking against a clear benchmark and evidence-based feedback are the most effective tools to overcome the better-than-average effect.

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