Goodhart’s law suggests that metrics change what’s measured.

The law is stated several ways, but two generalized forms are

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


When a measure becomes a target, it ceases to be a good measure.

Like in quantum physics, in some cases, the observation of a system can incorporate the observer and the behave differently as a result.rM7 In systems thinking, this may be called policy resistance as the controller and the controlled circle one another seeking contrary goals. The Lucas critique suggests, less pessimistically than Goodhart, that rational actors’ reaction to policy change results in changed behavior, but that models can reflect responses as part of their design.rL7

  1. Robert E. Lucas, “Econometric Policy Evaluation: A Critique,” Carnegie-Rochester Conference Series on Public Policy, no. 1 (1976): 19–46. (See notes.)

  2. Michael McIntyre, “Goodhart’s Law,” October 17, 2001, (See notes.)