Campbell's Law

Campbell's Law is a social-scientific principle formulated by psychologist Donald T. Campbell in 1976, stating: 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. The law is a sociological counterpart to Goodhart's Law, with which it is often confused, but it carries a distinct emphasis: Campbell's Law applies specifically to social indicators — measures of crime, education, health, welfare — and to the political and institutional pressures that deform them.

The law predicts not merely gaming but systemic corruption. When test scores determine school funding, administrators manipulate who takes the tests, how the tests are administered, and how the results are reported. When crime statistics determine police promotions, departments reclassify felonies as misdemeanors, discourage reporting, and shift patrol patterns to produce favorable numbers. The corruption is not a bug but an adaptive response: the system is optimizing the metric because the metric is the system.

Campbell's Law has been invoked in critiques of accountability regimes, new public management, and evidence-based policy. It suggests that the demand for quantifiable outcomes in domains of inherent complexity — teaching, policing, social work — produces not better outcomes but better-looking outcomes, and that the gap between the two is itself a measure of institutional decay.

Campbell's Law is not an argument against measurement. It is an argument against the fantasy that measurement can replace judgment, or that quantitative accountability can substitute for qualitative trust. The systems that ignore it are not naive. They are complicit.