You keep using that word. I do not think it means what you think it means.

By Felix Salmon
January 28, 2013

This year’s Davos was all about tail risk — or, more to the point, the absence thereof. The ECB’s Mario Draghi said — more than once — that he had “removed the tail risk from the euro”. His colleague Ignazio Visco went almost as far, saying that only a few tail risks remain. The EU’s Olli Rehn talked about how there’s “no tail risk” any more. The IMF’s Zhu Min said that “In Europe, the tail risk has been moved off the table”, which was exactly the same language also used by Ray Dalio. Bank of America CEO Brian Moynihan said that “euro tail risk is now sorted”. The FT editorialized about the best policy response when “the tail risk of renewed financial chaos is reduced”. Even Nouriel Roubini declared that tail risks have declined in the past six months, although they haven’t gone away. And that was just the on-the-record comments: off the record, many more people, including at least one official US representative, were saying the same thing.

It was enough for both incoming Bank of England chief Mark Carney and UBS’s Alex Weber to start cracking jokes about how tail risks had been reduced on Wednesday and downright eliminated by Friday. As Stephanie Flanders says, Davos wouldn’t be Davos if people weren’t constantly talking about the need to avoid complacency — but for once, this year, “there seemed a genuine risk of it breaking out”.

There’s a worrying trend here, and it’s not complacency. Rather, it’s the use of the term “tail risk” to mean “priced-in and foreseeable euro crisis”. Last year, everybody was worried that Greece could end up leaving the euro, and those worries were reflected in European markets. This year, those worries have abated somewhat. But please, let’s not use the term “tail risk” to refer to such things.

We live in a fat-tailed world: everybody at Davos would probably agree on that. But here’s what none of them seem to understand: tail risks, by definition, can’t be measured. If you can look at a certain risk and determine that it has gone down, then it’s not a tail risk: it’s something else. Let’s say that last year there was a 25% chance that Greece would leave the euro: if something has a 25% chance of happening, it’s not a tail risk any more, it’s just a risk. If you’re planning a trip to the Grand Canyon, you might think about buying travel insurance to cover yourself in the event you are seriously injured. But when you’re right up at the edge of the canyon and the ground starts slipping beneath your feet, at that point you have to actually do something to avoid injury or death. The risk has gone from being theoretical to being real — and at that point it’s not a tail risk any more, it’s a real possibility with a scarily high probability.

The World Economic Forum spends many millions of dollars every year looking at risks both imminent and remote. It’s a useful exercise, and helps to remind us how complex the world is: with so many moving parts, it’s impossible for anybody to have much success as a predictor of the future. What’s not a useful exercise is to try to quantify the world’s risks, and to make determinations as to whether the tails are getting thinner.

And it’s certainly not a useful exercise, when markets have calmed down a little, to turn around and say that something as momentous as a fully-fledged euro crisis was only ever a “tail risk” to begin with. It wasn’t: it was much more imminent than that, and in order to avert it the EU had to venture far into the realm of policy actions which only a few months earlier would have been unthinkable. (Including effectively writing off a large amount of the money Greece owes the official sector.)

Tails are the realm of unknown unknowns. They can be positive, like the discovery of antibiotics, or they can be negative, like the uncovering of Bernie Madoff. In markets, they’re not even real-world events at all: they’re just any large move of say three standard deviations or more. Such moves happen almost every week, in some market somewhere, and they happen pretty much randomly. Measuring risks is good; seeing those risks diminish is pleasurable. But let’s not refer to measurable risks as “tail risks”. Because tail risks are always hidden, and unexpected.

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