The Original Goodhart's Law is More Interesting

Goodhart’s Law, named after economist Charles Goodhart, is commonly known as:

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

And this is a useful, pithy, and very relevant-to-the-current-times statement.

However, the original quote that eventually became Goodhart’s Law, is a good bit more interesting, in my opinion:

Any observed statistical regularity will tend to collapse once pressure is placed upon it for control purposes.1

This can reduce to the same form as above, but is more broad, and with this, also more applicable. A statistical anomaly does not necessarily have to be a measure in the common sense.2. Someone acting on a subjectively-felt frequency of an event, in order to control that event is going to fall under this as much as an someone being explicitly measured quarter targets and then finding ways to count various unrelated things against that target.

Similarly, it also does not say that the intended observation of it is subverted, but instead that the anomaly goes away, and now what used to be a discontinuity that was unusual is now what is expected. This is also a a broader thing, as what once was a discrete threshold (the anomaly) is now just part of a continuous range. Some controls can work absolutely fine with that, though the originally intended behaviour will change.

Third: Talking about “pressure” means also that there are various control measures that impose more or less pressure, and that there is a spectrum here: Controls can be light-weight and not cause the anomaly to collapse nearly as fast as making it the core measure of someone’s worth as, say, an employee. By changing the exact purpose for which the anomaly is used also makes it collapse more slowly, i.e., by not exclusively and immediately using it in a transparent manner for behaviour change, it can be preserved.

This is also where diagnostic metrics vs accountability metrics3 come in, not all control has to inspire a change of behaviour that makes the anomaly collapse.

There’s a great deal more nuance and also opportunity in the original quote from Goodhart that is lost when condensed. That’s usually fine, but I think that nuance can be very useful when trying to navigate well, nuanced situations.

  1. Goodhart, Charles (1975). “Problems of Monetary Management: The U.K. Experience”. In Courakis, Anthony S. (ed.). Inflation, Depression, and Economic Policy in the West. Totowa, New Jersey: Barnes and Noble Books (published 1981). p. 116. ISBN 0-389-20144-8. 

  2. Though it’s probably hard to recognise what is an anomaly without putting it into some form of measurement. 

  3. I wrote about this before, here