Survivorship bias — definition

What is survivorship bias?

Survivorship bias is a logical error that involves drawing conclusions based solely on "winners" — those who survived — while ignoring those who dropped out. In finance, this leads to systematically inflated expected returns.

Classic example: WWII aircraft

During World War II, mathematician Abraham Wald analyzed where to reinforce bomber aircraft. The military wanted to strengthen areas with the most bullet holes in returning planes. Wald pointed out the opposite — reinforce the places without holes, because planes hit in those places didn't return.

Survivorship bias in investing

Investment funds

Fund statistics look better than reality because:

• Funds with poor performance are closed or merged with others
• Rankings show only those that survived
• The average return of "funds in the market" is inflated by 1–2% annually

Stock indices

WIG20 or S&P 500 regularly replace companies. Weak companies drop out, strong ones enter. The historical chart of the index shows the path of "winners," not those who went bankrupt.

Success stories

We read about Buffett, Bezos, Musk — but not about thousands of investors and entrepreneurs who applied the same strategies and failed. This creates an illusion that success is easier than in reality.

Real estate

"Real estate always rises" — because we look at what survived. We don't see buildings that collapsed, ghost developments, or locations that lost value.

How survivorship bias distorts decisions?

• You overestimate chances of success — you only see winners
• You choose "hot" funds — based on incomplete data
• You copy millionaire strategies — not seeing how many people with the same strategy went bankrupt
• You ignore risk — because it's "not visible" in the data

How to avoid survivorship bias?

1. Ask about the absent — how many funds from this TFI were closed?
2. Look for data including closed funds — survivorship-free data
3. Don't copy blindly — that someone succeeded doesn't mean you will too using the same strategy
4. Invest passively — broad ETFs minimize this bias (you invest in the entire market)
5. Consider the base — how many tried vs. how many succeeded?

How Freenance can help

Freenance shows the complete picture of your portfolio — including investments that lost value. You don't hide failures, you see the real return rate of your entire portfolio and make decisions based on complete data.

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