Goodhart’s Law Applies To Economies, To Everything – Why Not Scheduled Airline Flight Times?


Which Magazine has stumbled across one of those “Yeah, Well?” things in its analysis of airline scheduled flight times. They’ve found that what the companies tell us will be the time taken to destination is longer now than it was a few decades back. There are two levels to the “Well?” part. The first being, well, fuel is more expensive so what do you expect? What do you actually want them to do? The second is Goodhart’s Law. That reason why no plan survives contact with the market place, no target actually works.

Plane journeys are taking longer than a decade ago, according to a report that claims the change is down to airlines “padding” their schedules to create the impression passengers were reaching their destinations on time.

Carriers are adding extra time to flight schedules, in some cases up to 30 minutes, to ensure they maintain punctuality and are therefore less likely to be liable for compensation payouts, the investigation by Which? Travel claimed.

The majority of flight routes are advertised as taking longer than 10 years ago, despite improvements in aircraft technology, the report found.

There have been improvements to aircraft technology, this is entirely true. Planes now sip a little less fuel to get somewhere, this achieved by their travelling just that little bit slower. Further, routes are now a little more carefully chosen to accord with winds and so on – things we know more about given better satellite and other monitoring technology. And fuel has become more expensive too, meaning that we’d actually like these hundreds of tonnes behemoths to be a little more sippy, sippy, in their consumption. We do actually desire the optimal trade off between the two costs, fuel and time expended and that optimal trade off depends upon the relative prices. When those relative prices change so does that optimal point.

So, good on the airlines then.

As to the idea that they’re extending reported times just to avoid having to pay compensation:

“Carriers are quick to claim that adding 10, 20 and even 30 minutes to flights will improve on-time performance. The accompanying slump in punctuality over recent years suggests it hasn’t helped much.

“Instead, longer scheduled flight times are likely to mean passengers spend more time sitting around at the gate or on the plane itself, just so the airline can pat itself on the back for being ‘on time’ at your destination.

“Conveniently, it could also reduce the number of instances when an airline has to pay you compensation for a flight delay.”

Fun that, no? They’ve extended flight times, it hasn’t increased punctuality, so we might therefore conclude that punctuality – as opposed to optimal trade off – isn’t the reason for the change. And yet the claim is still that they have. Hmm.

But now to introduce a much larger point, Goodhart’s Law. This is why planning an economy simply doesn’t work. Issue targets that must be hit and people game the system to hit the targets without actually doing the desired underlying thing. Or, as it is formally constituted:

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

Or as it has been reformulated:

Goodhart’s law is an adage named after economist Charles Goodhart, which has been phrased by Marilyn Strathern as: “When a measure becomes a target, it ceases to be a good measure.”[1] One way in which this can occur is individuals trying to anticipate the effect of a policy and then taking actions which alter its outcome.

Set a target for tonnes of shoes and you get one tonne shoes. Set a target for 100 shoes and you get 100 left feet. Set a target for being on time and people fiddle their definition of time.

It is, by the way, entirely fine to insist that airlines play fair with telling us how long a flight will take. You said it will take 4 hours, then 4 hours should be about the time it takes. Yes, sure, we understand, airports, crowded places. Idiot passengers forget to board, luggage must be taken off. Winds vary, thunderstorms happen, French air traffic controllers actually turn up to work today, their one day in seven. Sure, there’re lots of variables. But if you say it’s about four hours then it should be about four hours. Great.

But to complain that they pad their number a bit is ludicrous. We’re holding their feet to the fire, insisting that an underestimate will lead to financial costs. Thus, obviously, they will overestimate. That’s not really even Goodhart’s Law, that’s just human beings. But then, as we know, those who would plan everything don’t deal well with the existence of people, do they?