1. A short thread on Goodhart's Law and Campbell's law.

When natural scientists take measurements of a macroscopic physical system, the system does not respond by changing its behavior in ways that undermine the value of the measurements.

2. The central insight of both Goodhart's law and Campbell's law is that social systems are different.

When a social scientist quantifies a social process or phenomena, the act of collecting and sharing data can alter behavior in ways that undermine the measurements' value.

Campbell's law states:

"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." https://www.sciencedirect.com/science/article/abs/pii/014971897990048X?via%3Dihub

Goodhart's law posits that

"Any observed statistical regularity will tend to collapse once pressure is placed upon it for control purposes." https://books.google.com/books?id=OMe6UQxu1KcC&pg=PA111#v=onepage&q&f=false

Outside the context provided by Goodhart's article, it's not all that obvious what this quotation means. Anthropologist Marilyn Strathern rephrased Goodhart's law as a clear, concise adage:

"When a measure becomes a target, it ceases to be a good measure"
https://archive.org/details/ImprovingRatingsAuditInTheBritishUniversitySystem

Goodhart's law and Cambell's law are often treated as equivalent, but Campbell put greater emphasis on the pernicious consequences. Discussing educational assessment tests, he writes the following (emphasis added).

To highlight the distinction between Goodhart's law and Campbell's law, I propose a rephrasing of Campbell's law in the manner of Strathern's adage.

Goodhart's law (Strathern)

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

Campbell's law (Bergstrom)

"When a measure becomes a target, people do stupid shit."

By popular request, a SFW version.

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Goodhart's law (Strathern)

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

Campbell's law (Bergstrom)

"When a measure becomes a target, people do counterproductive things."