- It stands that a measure ceases to be a good measure when it becomes a target.
- Charles Goodhart advanced this idea in 1975.
- When we pick a feature of the economy as an indicator of the economy, it ceases to function as that indicator because people start to game it.
- The same happens to statistical variables.
- It's a [system mental model](/zettel/system-mental-models) because it explains how a system works when a measure becomes the target.
- Using multiples targets avoids Goodhart's Law because you must increase them all, not only one.
- If you measure people on the number of nails made, you might get many tiny nails. If you measure the weight of nails made, you might get a few giant and heavy nails.
- Educational systems that measure the students by grades incentivize them to memorize content for a test, then promptly forget it all.
- How do you avoid Goodhart's Law?
- [Wikipedia. Goodhart's law](https://en.wikipedia.org/wiki/Goodhart%27s_law)
- [Will Koehrsen. Unintended Consequences and Goodhart’s Law](https://towardsdatascience.com/unintended-consequences-and-goodharts-law-68d60a94705c)