Goodhart’s law

Once a useful number becomes a measure of success, it ceases to be a useful number. This is known as Goodhart’s law, and it reminds us that the human world can move once you start to measure it. Deborah Stone writes about Soviet factories and farms that were given production quotas, on which jobs and livelihoods depended.  

Numbers can be at their most dangerous when they are used to control things rather than to  understand them. Yet Goodhart’s law is really just hinting at a much more basic limitation of a data- driven view of the world … there’s a critical gap between even the best proxies and the real thing— between what we’re able to measure and what we actually care about.

Hannah Fry writing in The New Yorker