Survivorship Bias

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Devayani Vyavaharkar
Student (University), India

Survivorship Bias

We all have often seen articles like: "12 things successful people do differently'" or "20 tips from the world's most successful people". Logically speaking, if it helped them to attain success, it should also help us with a similar paradigm. However, such type of logic is structurally flawed. If we only take advice from successful people and ignore all failures, we will be left with a distorted view of reality. Such types of articles tend to focus only on survivors, i.e., the people who made it. They do not consider the thousands of others who followed their steps to become successful but are not successful today.

What is Survivorship Bias?

Survivorship bias, also known as survival bias, is the human tendency to focus only on survivors instead of everyone (including those who did not survive). This bias tends to focus our attention on winners and not losers, prosperous and successful, but not on a thousand others who worked hard but failed. Survivorship bias rules our lives in the way we focus our attention on successful CEOs, athletes, artists, and entrepreneurs for advice on how to live life and become successful. Very often, success is made more visible than failure, thus hiding it from plain sight. It leads us to overestimate our chance of succeeding as failures of the unsuccessful ones are ignored and conveniently forgotten.

History of Survivorship Bias

During World War 2, efforts were taken by the US military to determine the exact location for placing armor on aircraft and fighter planes to ensure their safety. An analysis of where the planes had been shot (picture) revealed that the central body, wingtips, and elevators needed to be armored. These areas showed the most number of bullet holes.
However, Abraham Wald, a statistician, disagreed. He argued the opposite, saying that engines, mid-body, and nose areas (the areas without bullet holes) should get better armors. Many considered this suggestion crazy, because planes were not hit at those places. In reality, planes getting shot in places described by Wald crashed and did not return. Hence, these planes could not be included in the collected data. The military believed that they had done a complete analysis of where planes suffered the most damage. However, they were not considering the whole sample, rather only the data from the survivors.

SURVIVORSHIP BIAS AND ITS APPLICATIONS

  • Investing / Stock markets: Successful stock traders and investors are frequently interviewed and asked for their success strategies. People tend to look at traders who survived while paying less attention to those that didn't.
    Edwin Elton, Martin Gruber, and Christopher Blake researched in 1976 on the impact of survivorship bias and mutual fund attrition. According to their research on 361 funds, most of the classic studies of mutual fund performance ignore attrition and are subject to survivorship bias. Results showed that a more significant percentage of small funds failed to survive and had poor performance as compared to substantial funds. Failure to eliminate survivorship bias leads to an overestimation of measured performance for the significant surviving funds.
  • Entrepreneurs: Both Steve Jobs and Bill Gates dropped out of college and started their own companies that were a huge success. Without any college education, they made it only following their passion and interests. Although it makes sense logically to follow their footsteps, our survivorship bias tends to distort our attention and makes us ignore the rest who had a unique business idea and dropped out of college too, but failed with their company.
  • Research: Research papers like those in the field of psychology gain recognition when they show significance. However, other papers that criticize them are often put away. Such kinds of trivial acts often lead to a rise in misconceptions, thus derailing progress.

STEPS TO ELIMINATE SURVIVORSHIP BIAS

  1. Take the advice of successful people with a grain of salt. Many people engage in the same things that successful people might have done. However, we do not hear about them, if it did not work out for them well.
  2. While analyzing data, it is essential to check the type of data one does not have. Very often, the full picture is hidden. Considering both sides of the same coin will help one make more rational and logical decisions.
  3. Try to be skeptical of books, resources, and motivational videos that present the secret formula for attaining wealth, happiness, and success.
In short, to eliminate survivorship bias we must remember to analyze the trajectories of those who did not succeed. It is tough to deal with survivorship bias, but we need to be conscious of our tendency to miss counter evidence.

⇒ Did you experience other remarkable management situations where survivorship bias was playing a disastrous role? Please comment below!

Sources:
Elton, E. J., Gruber, M. J., & Blake, C. R. (1996), "Survivor Bias and Mutual Fund Performance", Review of Financial Studies, 9(4), 1097-1120. DOI:10.1093/rfs/9.4.1097
Davies, J. (2020, June 11), "Survivorship Bias and 4 Examples of How It Can Distort Your Thinking".
Hughes-Jones, R. (2020, January 19), "How to avoid being duped by survivorship bias"

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