Suviviorship Bias


Tim Ferris published this book with an intention to help readers probe their ideas of work and achievement. Represented here are a few of the core ideas, and there is a link below to a much more comprehensive summary for those who would like to explore deeper. 


In World War 2, the American Air Force asked, could they improve the odds of a bomber making it home? Military engineers explained to the statistician that they already knew the allied bombers needed more armor, but there was a limit due to weight. 

The operational commanders asked for help figuring out the best places to add what little protection they could. The military looked at the bombers that had returned from enemy territory. They recorded where those planes had taken the most damage. Over and over again, they saw that the bullet holes tended to accumulate along the wings, around the tail gunner, and down the center of the body. Wings. Body. Tail gunner. 

Naturally, the commanders wanted to put the thicker protection where they could clearly see the most damage, where the holes clustered. 

The mistake, which Professor Wald saw instantly, was that the holes showed where the planes were strongest. The holes showed where a bomber could be shot and still survive the flight home, Wald explained. After all, here they were, holes and all. 

It was the planes that weren’t there that needed extra protection, and they had needed it in places that these planes had not. 

The holes in the surviving planes actually revealed the locations that needed the least additional armor. Look at where the survivors are unharmed, he said, and that’s where these bombers are most vulnerable; that’s where the planes that didn’t make it back were hit. 


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