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Monday, March 05, 2012

Tetlock podcast: expert predictions

I recently came across this excellent talk (podcast number 84 on the list at the link) by Philip Tetlock about his research on expert prediction.

Putting aside the fox vs hedgehog dichotomy, I think the main takeaway is that "expert" predictions are no better than those of well-informed ordinary people, and barely outperform simple algorithms.

Longnow.org: ... Tetlock took advantage of getting tenure to start a long-term research project now 18 years old to examine in detail the outcomes of expert political forecasts about international affairs. He studied the aggregate accuracy of 284 experts making 28,000 forecasts, looking for pattern in their comparative success rates. Most of the findings were negative— conservatives did no better or worse than liberals; optimists did no better or worse than pessimists. Only one pattern emerged consistently.

“How you think matters more than what you think.”

It’s a matter of judgement style, first expressed by the ancient Greek warrior poet Archilochus: “The fox knows many things; the hedgehog one great thing.” The idea was later expanded by essayist Isaiah Berlin. In Tetlock’s interpretation, Hedgehogs have one grand theory (Marxist, Libertarian, whatever) which they are happy to extend into many domains, relishing its parsimony, and expressing their views with great confidence. Foxes, on the other hand are skeptical about grand theories, diffident in their forecasts, and ready to adjust their ideas based on actual events.

The aggregate success rate of Foxes is significantly greater, Tetlock found, especially in short-term forecasts. And Hedgehogs routinely fare worse than Foxes, especially in long-term forecasts. They even fare worse than normal attention-paying dilletantes — apparently blinded by their extensive expertise and beautiful theory. Furthermore, Foxes win not only in the accuracy of their predictions but also the accuracy of the likelihood they assign to their predictions— in this they are closer to the admirable discipline of weather forecasters.

The value of Hedgehogs is that they occasionally get right the farthest-out predictions— civil war in Yugoslavia, Saddam’s invasion of Kuwait, the collapse of the Internet Bubble. But that comes at the cost of a great many wrong far-out predictions— Dow 36,000, global depression, nuclear attack by developing nations.

Hedgehogs annoy only their political opposition, while Foxes annoy across the political spectrum, in part because the smartest Foxes cherry-pick idea fragments from the whole array of Hedgehogs.

Bottom line… The political expert who bores you with an cloud of “howevers” is probably right about what’s going to happen. The charismatic expert who exudes confidence and has a great story to tell is probably wrong.

And to improve the quality of your own predictions, keep brutally honest score. Enjoy being wrong, admitting to it and learning from it, as much as you enjoy being right.

See also Intellectual honesty: how much do we know?

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