What Bullet Holes in Airplanes Can Teach You About Making Better Business Decisions:
During World War II, statistician Abraham Wald tried to determine where to add extra armor to airplanes. Based on the patterns of bullet holes in returning airplanes, he suggested that the parts not hit should be protected with extra armor. Why? Wald was looking at what is sometimes called "dead evidence." He reasoned like this... if these planes are returning, we know that if they are hit in the spots they have been hit, they can still fly. The planes that did not return must have been hit in different places. So put the extra armor wherever the returning planes were not hit. I think most people would have a natural inclination to put the armor where the returning planes had been hit. The real answer is simple, but counterintuitive. It's called "dead evidence" because it is what people ignore when they make these judgments.
During World War II, statistician Abraham Wald tried to determine where to add extra armor to airplanes. Based on the patterns of bullet holes in returning airplanes, he suggested that the parts not hit should be protected with extra armor. Why? Wald was looking at what is sometimes called "dead evidence." He reasoned like this... if these planes are returning, we know that if they are hit in the spots they have been hit, they can still fly. The planes that did not return must have been hit in different places. So put the extra armor wherever the returning planes were not hit. I think most people would have a natural inclination to put the armor where the returning planes had been hit. The real answer is simple, but counterintuitive. It's called "dead evidence" because it is what people ignore when they make these judgments.