Survivorship Bias — Abraham Wald and the WWII Planes

Survivorship bias is a tricky fal­lacy to deal with.

We’re all mes­mer­ised by suc­cess stor­ies. But study­ing those who are suc­cess­ful isn’t always the best idea.

You might suc­cumb to sur­viv­or­ship bias.
You might bet on flawed strategies.

Here we go:

Abraham Wald and the WWII Planes

During World War II, the Allies stud­ied Nazi dam­age to their fight­er planes. Their study res­ul­ted in this dot­ted illustration:

The ana­lys­is of these dam­ages res­ul­ted in the idea that the Allied Forces should rein­force their fight­er planes in the areas show­ing the densest clusters of red dots. 

A stat­ist­i­cian by the name of Abraham Wald dis­agreed. Instead, he sug­ges­ted that they rein­force sur­faces with no red dots. Wald was right, of course. The red-dot­ted areas indic­ated non-fatal dam­aged regions by study­ing planes that some­how returned home. 

If it had been pos­sible to study all the planes shot down and des­troyed by the Nazis, maybe the research team would have found an inverse pattern?

“Wald’s work on air­craft vul­ner­ab­il­ity, using data from sur­viv­ors, was cru­cial in World War II, Korea, and Vietnam, and has been reis­sued by the Center for Naval Analyses.”
Source: Journal of the American Statistical Association ¹Mangel, M., & Samaniego, F. (1984). Abraham Wald’s Work on Aircraft Survivability. Journal of the American Statistical Association, 79, 259 – 267. https://​doi​.org/​1​0​.​1​0​8​0​/​0​1​6​2​1​4​5​9​.​1​9​8​4​.​1​0​4​7​8​038

WWI and the Soldiers’ Helmets

In anoth­er example, we focus on a seem­ingly coun­ter­in­tu­it­ive phe­nomen­on that emerged dur­ing World War I. 

As mil­it­ary forces began to issue more hel­mets to sol­diers to pro­tect them from the per­ils of the bat­tle­field, an unex­pec­ted trend was observed: the num­ber of wounded sol­diers surged dramatically.

At first glance, it may seem that the hel­mets were para­dox­ic­ally mak­ing it easi­er for more people to get hurt. The crux of this para­dox lies in the shift­ing dynam­ics of the cas­u­alty statistics: 

As hel­mets were intro­duced and dis­trib­uted more widely, they sig­ni­fic­antly reduced the num­ber of fatal­it­ies on the bat­tle­field. Soldiers who would have pre­vi­ously suc­cumbed to their injur­ies were now sur­viv­ing. Consequently, these sol­diers were clas­si­fied as “wounded” rather than “dead.”

This shift in cat­egor­isa­tion cre­ated the illu­sion of increased injur­ies when, in real­ity, the num­ber of fatal­it­ies had decreased. 

The Fallacy of Survivorship Bias

These examples under­score the import­ance of con­sid­er­ing the lar­ger con­text and being cau­tious about con­clu­sions based solely on super­fi­cial data.

Both stor­ies are excel­lent examples of a par­tic­u­lar fal­lacy — sur­viv­or­ship bias.

“Survivorship bias, sur­viv­al bias is the logic­al error of con­cen­trat­ing on entit­ies that passed a selec­tion pro­cess while over­look­ing those that did not. This can lead to incor­rect con­clu­sions because of incom­plete data.”
Source: Wikipedia ²Survivorship bias. (2023, October 9). In Wikipedia. https://​en​.wiki​pe​dia​.org/​w​i​k​i​/​S​u​r​v​i​v​o​r​s​h​i​p​_​b​ias

We often can’t help being enticed by suc­cess stor­ies in pop­u­lar cul­ture and busi­ness. But their stor­ies can lead us to fal­la­cious conclusions. 

Few think about study­ing those who turn out to be unsuc­cess­ful. This is too bad for data sets since the unsuc­cess­ful typ­ic­ally out­num­ber the suc­cess­ful by a vast margin.

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• 58 Logical Fallacies and Cognitive Biases
• Social Group Sizes (The Social Brain Hypothesis)
• The Pitfalls of Groupthink: Decision-Making in Organisations
• Cognitive Dissonance: Mental Harmony Above All Else
• Survivorship Bias — Abraham Wald and the WWII Airplanes
• The Engagement Pyramid (The 90−9−1 Principle)
• 150 — Dunbar’s Number
• Theory of Mind: A Superpower for PR Professionals
• The Amplification Hypothesis: Counter Extreme Arguments
• The Baader-Meinhof Phenomenon: Heard About It Before?
• The Halo Effect: Why Attractiveness Matters in PR
• The Paradox of Prominence
• Parkinson’s Law & The Law of Triviality (Bike Shed Effect)
• Diffusion of Innovations

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