Not Everything That Counts Can Be Counted And Not Everything That Can Be Counted Counts


During World War II, lots of fighter planes were getting hit by anti-aircraft guns. Air Force officers wanted to add some protective armor/shield to the planes. The question was where? The planes could only support few more kilos of weight.

A group of mathematicians & 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/sq. foot near the tail of the planes whereas only 1.11 bullet holes/sq. foot close to the engine.

The Air Force officers 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 aren’t – around the engines.

His judgment surprised everyone. He said “We are counting the planes that returned from a mission. Planes with lots of bullet holes in the engine did not return at all”.

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