Goodhart's Law

Goodhart's law, although it can be expressed in many ways, states that once a social or economic indicator or other surrogate measure is made a target for the purpose of conducting social or economic policy, then it will lose the information content that would qualify it to play that role. The law was named for its developer, Charles Goodhart, a former advisor to the Bank of England and Emeritus Professor at the London School of Economics.

The law was first stated in a 1975 paper by Goodhart and gained popularity in the context of the attempt by the United Kingdom government of Margaret Thatcher to conduct monetary policy on the basis of targets for broad and narrow money, but the idea is considerably older. Closely related ideas are known under different names, e.g. Campbell's Law (1976), and the Lucas critique (1976). The law is implicit in the economic idea of rational expectations. While it originated in the context of market responses the Law has profound implications for the selection of high-level targets in organisations.

It has been asserted that the stability of the economic recovery that took place in the United Kingdom under John Major's government from late 1992 onwards was a result of Reverse Goodhart's Law: that, if a government's economic credibility is sufficiently damaged, then its targets are seen as irrelevant and the economic indicators regain their reliability as a guide to policy.