What Is the Survivorship Bias and Why Should I Care?

By Eric Dean JD, MBA, MA, MA, LPC, CADC

I am going to share with you a story about a brilliant mathematician named Abraham Wald. During World War II, Wald was employed at the Statistical Research Group (SRG) at Columbia University where he helped the United States develop wartime strategy. Wald was tasked with assessing the damages to returning aircraft (not all aircraft made it back) and recommending ways to minimize damage to departing aircraft by adding armor to the planes. However, because aircraft armor is so heavy, adding it to the entire plane would negatively impact the plane’s performance and be cost prohibitive. Therefore, SRG would need to determine to which parts of the plane it should add armor.  

The team examined the bullet holes in the returning planes and noticed that there was the greatest concentration in the wings. Officers suggested to add armor in this area because it is where the planes sustained the most damage. Many others agreed, but not Wald. Wald suggested the opposite: that armor should be added to the area of the plane where there was the least amount of bullet holes – the engine. Wald realized that the officers were drawing a conclusion based on an incomplete sample of only planes that returned or survived. He concluded that the concentration of bullet holes in returning planes showed where they could sustain the most damage and they incurred the least damage to the engine because planes with extensive engine damage did not return. Therefore, Wald’s recommendation was to add armor to the engine, not the wings. His insight saved thousands of lives during the war and today has numerous applications in military strategy, clinical research, manufacturing, and financial markets, among others.  

This story is a great illustration of the survivorship bias. The survivorship bias, according to The Decision Lab, is “…a cognitive shortcut that occurs when a visible successful subgroup is mistaken as an entire group, due to the failure of the subgroup not being visible.” The officers in the example above only studied damages to returning planes (“survivors”) but failed to consider the damages sustained by the many planes which did not return.

So why am I sharing this with you?

As a therapist, I help my clients achieve their goals. There are many factors that can impact a client’s plan, or process, for moving from their current state to their desired state. For example, take someone whose goal is to start a small business. Part of their plan is to identify others, like themselves, who have succeeded in this area and then emulate those qualities and behaviors. While this may be a good starting point, there is a survivorship bias when we only look at similarly situated people who have succeeded (“survivors”) and not similarly situated people who have failed. This is due, in part, to the fact that small business success stories are much more visible than small business failures. But for every successful small business, how many similar ones have failed?

Just because some information is more difficult to obtain, does not make it any less important than information which is readily available and accessible, for making an informed decision.  When we only study successes, we draw incorrect conclusions and become unreasonably optimistic about our ability to succeed. For example, if we examine common traits of successful small business owners, we may find that they possess higher than average charisma. However, just because they may be charismatic, does not mean that their charisma caused them to be successful. There were probably a lot of charismatic individuals whose businesses failed.

A Symmetry therapist can help you cultivate awareness of how your perceptions may be affecting your ability to accurately define the challenges in your life. And, together, we can use Wald’s insight to determine the best way to go about achieving your goals. 

So, let’s get started – call Symmetry Counseling in Chicago today at 312-578-9990.

Reference

Ellenberg, Jordan. How Not to Be Wrong: The Power of Mathematical Thinking. Penguin Books, 2015.

“Survivorship Bias – Biases & Heuristics.” The Decision Lab, 22 Jan. 2021, thedecisionlab.com/biases/survivorship-bias/.