In 1975, the economist Charles Goodhart wrote an article on monetary management in the United Kingdom. In it he observed: “Any observed statistical regularity will tend to collapse once pressure is placed upon it for control purposes.”
The idea became known as Goodhart’s law. A common wording of it appears in a 1997 paper by Marilyn Strathern on audit in British universities: “When a measure becomes a target, it ceases to be a good measure.”