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DATA versus Intelligent Analysis

Author: Jordan Ellenberg

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During World War II, numerous ghter planes were getting hit by anti-aircraft guns. Air Force Ofcers wanted to add some protective armor/shield to the planes. The question was “where”? The planes could support only a few more kilos of weight.

A group of mathematicians and engineers were called for a short consulting project. Fighter planes returning from missions were analyzed for bullet holes per square foot. They found 1.93 bullet holes / square foot near the tail of the planes whereas only 1.11 bullet holes/square foot close to the engine. The Air Force Ofcers thought that since the tail portion had the greatest density of bullets that would be the logical location for putting an anti-bullet shield. A mathematician named Abraham Wald said exactly the opposite: more protection is needed where the bullet holes are less -- that is -- around the engines. His j u d g m e n t s u r p r i s e d everyone. He said, "We are counting the planes that r e t u r n e d f r o m a m i s s i o n . Planes with lots of holes in the engine d i d n o t return at all."

Debrief
If you go to the Recovery Room at the hospital you'll see a lot more people with bullet holes in their legs than people with bullet holes in their chests. That is not because people don't get shot in the chest, it's because the people who get shot in the chest don't recover.

Remember the words of Einstein: “Not everything that counts can be counted, and not everything that can be counted counts”.

Story source from the book “How Not To Be Wrong” by Jordan Ellenberg. Contributed by Shireen Hussain

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