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Expert Political Judgement: How Good Is It?

Philip Tetlock

Weather forecasts. Would it be all right with you if I made a quick point about them, provided that I don't go on and on about it? I promise you that I am not intending to attempt an extended metaphor involving the economy and severe storms.

The thing about weather forecasts, you see, is this - you can't forecast the weather. I apologise if this seems a rather fundamental objection. All you can do is provide a probability of experiencing different weather conditions. As the event comes nearer, the confidence you can invest in your forecast will usually rise. And that's it. Yet there's little of this when you listen to a forecast, is there? There's just stuff about requiring your umbrella. It's all most annoying.

Anyway, I'm glad to have got that out of the way because I am about to make a political forecast, something that I rarely do, and I want you to understand me correctly. You can't make political forecasts any more than you can make weather forecasts. All you can do is talk of probabilities.

And most political experts aren't even very good at that. In 2005, Philip Tetlock published his eye-opening book Expert Political Judgment: How Good Is It? The volume provides the result of a 20-year study of 28,000 predictions made by 284 pundits, political academics and theorists. It turns out that the experts barely did better than random guesses. The more prominent the pundit, the worse the estimate. Very basic computer models did far better.

The reason for such a poor performance is twofold. The first is that human affairs are highly unpredictable, being more complicated and more vulnerable to chance even than the weather. The second is that experts over-complicate things, attaching great importance to matters that they know about, even when those are not critical to the outcome. A striking feature of Professor Tetlock's study is that experts usually did better making political predictions outside their area of greatest expertise.

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