Goodhart's law: why a number stops telling the truth once it becomes a target
Goodhart's law: when a measure becomes a target, it stops being a good measure
A number that told the truth for years starts to lie the day a bonus rides on it, and nobody cheated. The economist Charles Goodhart saw the same thing at the Bank of England in 1975.
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Miva won the bonus, riders are stuck, and nobody lied. Think back to before the bonus: nobody steered the time to close, so it rose and fell with the help riders got, and it told you how they were doing.
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Once it paid, it followed the quickest road instead, lock open or not. The number still moved, but it no longer moved with the goal.
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You're not the first to see it. In 1975, the economist Charles Goodhart, an adviser to the Bank of England, saw it with money. The Bank watched how much money was in the country, and once it tried to push that number, the number stopped moving the way it always had.
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Years later, the anthropologist Marilyn Strathern put the idea in the words people quote today. It still carries his name: Goodhart's law.
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So you look for a number that's harder to bend: 1 to 5 stars from the rider after each chat. From next month, the bonus pays for speed and stars. Two numbers can't both be gamed, can they?
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Go further
Where the two famous names first wrote about it.