At around the same time that Goodhart proposed his law, psychologist Donald Campbell independently proposed an analogous 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. Campbell illustrated his principle with the case of standardized testing in education: Achievement tests may well be valuable indicators of general school achievement under conditions of normal teaching aimed at general competence. But
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