Goodhart's Law: When a measure becomes a target, it ceases to be a good measure

This is probably where I should mention my two longer articles that discuss this in depth; https://www.ribbonfarm.com/2016/06/09/goodharts-law-and-why-... https://www.ribbonfarm.com/2016/09/29/soft-bias-of-underspec... As well as my more recent paper categorizing the different ways it occurs; https://arxiv.org/abs/1803.04585

A closely-related effect I often cite is the McNamara fallacy[0], which is essentially about the tendency to focus on aspects of a system that are easily measurable, often at the expense of aspects that are not. I see it as one of the weaknesses of the data-driven decision-making movement, since many interpret "data" to mean "numbers". I think this fallacy can partly explain why Goodhart's Law holds: it's the non-measurable (or difficult-to-measure) aspects that suffer most when a metric becomes…

Goodhart’s law: “Any observed statistical regularity will tend to collapse once pressure is placed upon it for control purposes.” And Marilyn Strathern’s generalization of it: “When a measure becomes a target, it ceases to be a good measure.” What are some examples of Goodhart’s Law that you see in the world?

It reminds me of that old saw falsely attributed to W E Deming, "If you can't measure it, you can't manage it". I often see it come up on twitter, usually quoted by people whose... managerial ambitions I would prefer thwarted for the greater good :P On the contrary Deming himself was very aware of this effect, and explicitly cautioned against running a company on just the numbers.