Goodhart's Law

A Goodhart's Law is an adage stating that when a measure becomes a target, it ceases to be a good measure.

• Context:
  • It can typically be quoted in Marilyn Strathern's 1997 wording, which she credited to Keith Hoskin's statement of Goodhart's point.
  • It can typically be explained by people optimizing their actions within a system of rewards, for example an employee rewarded by the number of cars sold who sells more cars even at a loss.
  • ...
  • It can often be applied to accountability and audit systems in organizations.
  • It can often be applied to research assessment, where citation-based measures become targets.
  • ...
  • It can range from being stated about statistical regularities used for monetary control to being stated about any measure used as a target.
  • ...
  • It can be traced to Charles Goodhart's 1975 article on monetary policy in the United Kingdom, which stated that any observed statistical regularity will tend to collapse once pressure is placed upon it for control purposes.
  • It can be related to Campbell's Law, which has earlier formulations, and to the Lucas Critique.
  • It can explain the ML Evaluation Pitfall in which a benchmark metric becomes the target of model development.
  • ...
• Example(s):
  • Goodhart's original observation about statistical regularities relied on for monetary control in the United Kingdom.
  • Marilyn Strathern's example that the more a 2.1 examination performance becomes an expectation, the poorer it becomes as a discriminator of individual performances.
  • Jon Danielsson's corollary for financial risk modelling: a risk model breaks down when used for regulatory purposes.
  • citation impact measures that are gamed once they are used to judge scientific publications.
  • ...
• Counter-Example(s):
  • a Conway's Law, which is an adage about organizations whose system designs copy their communication structures, not about measures used as targets.
  • a Surrogate Endpoint, which is a measure deliberately used in place of another, rather than the claim that targeting a measure degrades it.
  • an Ironies of Automation, which is a thesis about automation and its operators rather than about measures and targets.
• See: Campbell's Law, Lucas Critique, ML Evaluation Pitfall, Organizational Key Performance Indicator (KPI) Measure, Surrogate Endpoint.

---

---

References

2026

• (Wikipedia, 2026) ⇒ https://en.wikipedia.org/wiki/Goodhart's_law Retrieved:2026-10-08.
  • QUOTE: Goodhart's law is an adage that has been stated as, "When a measure becomes a target, it ceases to be a good measure". 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:

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

  • QUOTE: ... Notably, Campbell's law likely has precedence, as Jeff Rodamar has argued, since various formulations date to 1969. ... Shortly after Goodhart's publication, others suggested closely related ideas, including the Lucas critique (1976). As applied in economics, the law is also implicit in the idea of rational expectations, an economic theory that those aware of a system of rewards and punishments will optimize their actions within that system to achieve their desired results. For example, if an employee is rewarded based on the number of cars sold each month, they will try to sell more cars, even at a loss. ...
  • QUOTE: ... Jon Danielsson states the law as

    Any statistical relationship will break down when used for policy purposes.

    And suggested a corollary for use in financial risk modelling:

    A risk model breaks down when used for regulatory purposes.

    Mario Biagioli related the concept to consequences of using citation impact measures to estimate the importance of scientific publications ...

1997

• (Strathern, 1997) ⇒ Marilyn Strathern. (1997). “‘Improving Ratings’: Audit in the British University System.” In: European Review, 5(3).
  • QUOTE: When a measure becomes a target, it ceases to be a good measure. The more a 2.1 examination performance becomes an expectation, the poorer it becomes as a discriminator of individual performances. Hoskin describes this as 'Goodhart's law', after the latter's observation on monetary control instruments, which led to the invention of other devices for monetary flexibility. ...
  • ABSTRACT: This paper gives an anthropological comment on what has been called the ‘audit explosion’, the proliferation of procedures for evaluating performance. ... While the metaphor of financial auditing points to the important values of accountability, audit does more than monitor—it has a life of its own that jeopardizes the life it audits. ...

---