Goodhart's Law

The Core Insight

Goodhart's Law identifies a fundamental paradox of measurement: the act of measuring and rewarding a specific metric changes the behavior of the people being measured. They optimize for the metric itself rather than the underlying goal the metric was meant to represent.

"Any observed statistical regularity will tend to collapse once pressure is placed upon it for control purposes." — Charles Goodhart^[1]

Classic Examples

Soviet Nail Factory

The Soviet government set a production target for nail factories measured by weight. Factories responded by producing a single, massive nail — meeting the weight target but producing something useless. When the target switched to quantity, factories produced millions of tiny, unusable nails. The workers were efficient at hitting the target but completely ineffective at the actual goal.

Healthcare Waiting Times

When the UK's NHS set a target that no patient should wait more than four hours in A&E, hospitals met the target by keeping patients in ambulances outside the hospital until a bed opened — the wait time inside didn't start until the patient entered. The metric improved; the patient experience did not.

Education

When schools are measured by standardized test scores, teachers teach to the test. Scores rise, but deeper learning and critical thinking decline. The measure improves while the goal (education) suffers.

Relationship to Efficiency vs. Effectiveness

Goodhart's Law is the mechanism by which the "Efficient but Ineffective" quadrant in The Difference Between Efficiency and Effectiveness arises:

• Efficiency metrics (cost per unit, cycle time, throughput) are seductive because they are easy to measure and compare.
• When these become targets, people optimize for them — often at the expense of the actual goal.
• The result: a highly efficient process that produces the wrong outcome.

Drucker's insight — "no amount of efficiency can compensate for a lack of effectiveness" — is Goodhart's Law at the strategic level. The metrics you choose to track will shape behavior, for better or worse.

Related Principles

Campbell's Law

Donald T. Campbell independently formulated a similar principle: "The more any quantitative social indicator is used for social decision-making, the more subject it will be to corruption pressures and the more apt it will be to distort and corrupt the social processes it is intended to monitor."^[2]

The McNamara Fallacy

The McNamara Fallacy is a specific case of Goodhart's Law applied to military strategy — measuring what is quantifiable (body counts) while ignoring what matters (strategic victory).

Cobra Effect

A colonial-era anecdote: the British government, concerned about venomous cobras in Delhi, offered a bounty for every dead cobra. Citizens began breeding cobras to claim the bounty. When the program was cancelled, the breeders released their now-worthless cobras, increasing the wild cobra population. The intervention made the problem worse.

Defending Against Goodhart's Law

1. Use multiple metrics — no single measure should dominate.
2. Measure outcomes, not outputs — effectiveness over efficiency.
3. Rotate metrics periodically — prevent gaming of any single target.
4. Include qualitative indicators — customer satisfaction, peer review, long-term impact.
5. Be suspicious of what is easy to measure — the most important things are often the hardest to quantify.

See Also

• The Difference Between Efficiency and Effectiveness — The Drucker distinction that frames why metric choice matters.
• The McNamara Fallacy — A historical case study of Goodhart's Law in military strategy.
• The Balanced Scorecard (Kaplan & Norton) — A framework designed to resist Goodhart's Law by using multiple, balanced metrics.
• Satisficing (Herbert Simon) — An alternative to optimization that avoids the perverse incentives of single-metric targets.

References