When traders look at long-term index performance charts, it’s tempting to assume they reflect the “true” experience of investors over time. But there’s a hidden distortion baked into indices like the S&P 500 and Russell 2000: survivorship bias. This bias occurs because failing companies are regularly removed and replaced by stronger firms, making historical index performance look healthier than what an actual buy-and-hold investor might have experienced.
How Survivorship Bias Skews the S&P 500
The S&P 500 is marketed as a snapshot of the 500 largest U.S. companies, but the membership list is far from static. Every year, dozens of names are swapped in and out. Companies that go bankrupt or underperform are removed, while stronger or fast-growing companies are added.

The SP500 index with major stocks removed at the height of the financial crisis
Consider the S&P 500 in 2007. Back then, financial giants like Lehman Brothers, Bear Stearns, and Washington Mutual were all part of the index—until the financial crisis exposed their fragility. Those stocks went to zero, but the historical chart of the S&P 500 smooths over their collapse because new leaders like Amazon, Nvidia, and Tesla later replaced them. The result: the long-term S&P 500 chart looks like a steady upward march, when in reality, an investor in the 2007 version of the index would have faced far more volatility and permanent capital loss in certain holdings.
This explains why the index’s backward-looking return can feel disconnected from the lived experience of investors who actually held the stocks in those earlier lineups.
The Russell 2000: Why It’s Barely Moved in 5 Years

The Russell 200 chart from late 2020 to current
The Russell 2000 highlights survivorship bias in another way. Unlike the S&P 500, which rotates in stronger companies, the Russell is composed of small-cap stocks, many of which don’t survive or struggle to grow consistently.
Over the past five years, the Russell 2000 has barely moved, stuck in a sideways range, even while the S&P 500 has marched higher. Why? Because many small caps in the Russell 2000 face structural challenges—thin margins, high debt, vulnerability to rising interest rates—that prevent them from compounding like large-cap tech stocks. Although the Russell swaps out some names, the sheer number of struggling companies means the index reflects more of the “grind” of small-cap reality. Survivorship bias here doesn’t create the same illusion of strength—it highlights stagnation instead.
Why This Matters for Traders
Survivorship bias creates a dangerous blind spot: it makes past returns look better than what an investor might have achieved if they actually owned the index’s constituents at the time.
- For the S&P 500, it means that long-term performance charts hide the graveyard of failed companies. The winners dominate the narrative, but the losers were just as real for investors who held them.
- For the Russell 2000, it means traders need to be aware that many of its members are structurally weak, which can cap index-level returns despite occasional rallies.
How Traders Can Navigate Survivorship Bias
- Dig Into Index Components – Don’t just look at the headline number. Study which sectors and companies are driving the gains or stagnation.
- Use Equal-Weight Alternatives – The S&P 500 Equal Weight Index provides a different perspective, diluting the effect of mega-cap leaders and better reflecting the average stock’s performance.
- Blend With Sector/ETF Analysis – Instead of relying only on broad indices, drill down into sector ETFs or specific trading groups to uncover true leadership and laggards.
- Keep Survivorship in Mind – When backtesting or studying history, remember the S&P 500 of 2007 is not the same as today’s. Adjust your expectations accordingly.
Equal-Weighted vs Cap-Weighted Indices: Why the Difference Matters
Most traders are familiar with the standard S&P 500, but fewer realize it’s a market-cap weighted index. That means larger companies (like Apple, Microsoft, Nvidia, and Amazon) dominate its movements. A 5% swing in Apple carries far more weight than a 5% move in a mid-cap stock buried deep in the index. Over time, this weighting system concentrates returns in a handful of mega-cap leaders, amplifying the survivorship bias effect: the winners shape the chart, while the losers fade into irrelevance.
By contrast, the S&P 500 Equal Weight Index treats every company the same, regardless of size. Each stock counts for 0.2% of the index at rebalancing. This approach provides a more balanced view of how the average stock in the S&P is performing. During periods when mega-cap tech leads the market (like the last several years), the equal-weight index lags behind the cap-weighted S&P. But in broad-based rallies where many sectors participate, the equal-weight version often outperforms.

This chart compares the SPY ETF, a perfect surrogate for the SP500 index vs RSP, the Rydex SP500 Equal Weighted ETF. Total return for SPY from the end of 2021 was around 38%. For the RSP it was 15% for the same period.
Why This Matters for Traders
- Cap-Weighted Bias – The standard S&P 500 often hides the struggles of most companies because the top 5–10 stocks drive the majority of returns.
- Equal-Weight Reality Check – Equal weighting exposes whether the rally is broad or narrow. If the equal-weight index is flat while the cap-weighted index surges, it’s a sign that leadership is very concentrated.
- Practical Application – Traders can compare the two versions (SPX vs RSP) to gauge market health. A wide gap between them signals that survivorship bias and concentration are distorting the headline numbers.
Final Thoughts
Market indices are invaluable tools, but they aren’t perfect mirrors of reality. Survivorship bias smooths over failures, amplifies winners, and sometimes hides the real risks of buy-and-hold investing. By understanding how indices evolve—and by analyzing beneath the surface—traders can avoid being lulled into a false sense of security and make smarter, more grounded trading decisions.