Goodhart's law

Adage about statistical measures / From Wikipedia, the free encyclopedia

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Goodhart's law is an adage often stated as, "When a measure becomes a target, it ceases to be a good measure".[1] It is named after British economist Charles Goodhart, who is credited with expressing the core idea of the adage in a 1975 article on monetary policy in the United Kingdom:[2]

Any observed statistical regularity will tend to collapse once pressure is placed upon it for control purposes.[3]

Charles_Goodhart_delives_the_2012_Long_Finance_conference_keynote_speech.JPG
Charles Goodhart, for whom the adage is named, delivering a speech in 2012

It was used to criticize the British Thatcher government for trying to conduct monetary policy on the basis of targets for broad and narrow money,[4] but the law reflects a much more general phenomenon.[5]