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.” 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?
Tim Worstall, “Goodhart’s Law Applies To Economies, To Everything – Why Not Scheduled Airline Flight Times?”, Continental Telegraph, 2018-08-27.
December 14, 2020
QotD: Goodhart’s law
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