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The bullet holes nobody saw saved the bombers.

In the Second World War the US military wanted to armour planes where returning aircraft had the most bullet holes. Statistician Abraham Wald objected: those planes had made it home despite the hits. The armour belonged where there were no holes, because planes hit there never came back. You only see the survivors.

Useful: For every success story, ask how many did the same thing and failed.

Source: en.wikipedia.org

BiasStatistik

Difficulty:

Question on this card

Where did Abraham Wald recommend armouring the bombers?

  1. Where most bullet holes were
  2. Where there were no bullet holes
  3. Evenly everywhere
  4. Only the cockpit
Show the answer

Correct: Where there were no bullet holes

Planes hit in those spots never returned, so they were missing from the sample.

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