Goodhart's Law

I am obsessed with Goodhart's Law. Once you know about it, you see it everywhere.

What is it? Let's ask Wikipedia:

Goodhart's law is an adage often stated as, "When a measure becomes a target, it ceases to be a good measure".^[1] It is named after British economist Charles Goodhart, who is credited with expressing the core idea of the adage in a 1975 article on monetary policy in the United Kingdom:^[2]

Any observed statistical regularity will tend to collapse once pressure is placed upon it for control purposes.^[3]

It was used to criticize the British Thatcher government for trying to conduct monetary policy on the basis of targets for broad and narrow money,^[4] but the law reflects a much more general phenomenon.^[5]

Well, that was helpful. Let me try my own worked example.

• You want to reward some behaviour. Let's say you're the government, and you think that people who go to A&E shouldn't have to wait for hours to be seen.
• You do this because constituents keep telling you that they're unhappy about it. There are stories in the papers. But people can be unhappy about all sorts of things, and papers can always find stories to tell, so first you decide to collect some data.
• You ask hospitals to measure how long it takes between a patient checking in at A&E and when they first talk to a doctor. They do this, and you find that the average time to be seen is, like, hours. Some hospitals are better than others, of course. This is your measure.
• So you now have a number you want to decrease. You want people to be seen sooner! You tell hospitals that they'll get in trouble if their number is too high - investigations, reduced funding, general bad career prospects for administrators who make the number get bigger. Now it's become a target.
• The hospital administrators put pressure on staff to try to get that number lower. Career prospects, investigations, etc.
• So now, in some hospitals, procedures change and after patients get admitted, they often have a quick chat with a doctor. And then they have to wait for a few extra hours to get actual treatment. Or patients arrive, and if they don't look like they're about to keel over then and there, have to wait half an hour until they get officially registered as having arrived at A&E.
• And now the number has become quite detached from the thing it was supposed to be incentivising. Some hospitals don't change their procedures, and have a high number. Some do, and have a low number. Some hospitals just see everyone quickly! The measure has stopped measuring the thing it was supposed to measure.

So now you're probably like... well, there must be a better way to measure that. And, probably there is. But the mechanism that ruins that measure will probably apply to your new version, too.

Or maybe you're like... well, sounds like regulating hospitals is hard but that's not my job. Glad I don't have to think about it! I'm not the government! But like I said, once you know about it, you see it everywhere.

Here's two examples that I've come across recently. First, we have this vintage post from Neil Kulkarni, three rants about the state of being a teacher and the lack of trust inherent in the system these days:

Three thoughts on Education.

Compiled from various thoughts/postings over 16 years of teaching thus far. Sad thing is - it all still holds.

Neil Kulkarni's Too Much MusicNEIL KULKARNI

And, spoilers, it's talking about the corrosive effect of being downstream of people attempting to apply targets towards education. Education is especially tricky here because the job is to turn children into better adults, and so the results are only seen decades from now.

But for our second example, let's take a swerve completely away from government, and instead look at a baffling thing someone on a Discord I'm on just got served as an Insta ad.

It is... a large face cuff. Whatever that is (it's jewellery, a bangle with a big flat bit on the top). And lots of people are being advertised it, not just my friend - I linked to a Reddit post where other people are talking about it, and are similarly baffled.

So, how does this connect to Goodhart? Here's my theory:

• M&S wants to sell stuff online. To do this they need people to buy their stuff.
• To find these people, they advertise on Instagram. They could make glossy ads... but actually, maybe it's better to just put the products up. The products are what they want to sell.
• So they hook up their online catalog with Meta's advertising tools (or probably a third party ad-tech tool, which I don't know about and don't want to). All the things, all the photos, are now available to be adverts.
• And they try them all! And they measure - hey, how many people clicked on this? It's a good proxy for "how many people bought this?", as, y'know, you gotta click it to buy it. But it's easier to measure - more people click than buy.
• And the large face cuff is just... baffling. So people click, to figure out what it is. And then probably don't buy it. Because they didn't like it, they just didn't understand it.
• Which makes it get promoted more. And shown to more people. Including my friend Charlotte.
• (The side effect is that Meta gets more money from showing adverts that don't sell anything. Speculation on what this does to Meta's incentives to build a better ad platform is left as an exercise for the reader)

Like I said, once you know about it, you see it everywhere.