Superforecasting: The Art and Science of Prediction

by Philip E. Tetlock

Kent couldn’t overcome such political barriers, but as the years passed the case he made for using numbers only grew. Study after study showed that people attach very different meanings to probabilistic language like “could,” “might,” and “likely.” Still the intelligence community resisted. Only after the debacle over Saddam Hussein’s supposed weapons of mass destruction, and the wholesale reforms that followed, did it become more acceptable to express probabilities with numbers. When CIA analysts told President Obama they were “70%” or “90%” sure the mystery man in a Pakistani compound was Osama bin Laden, it was a small, posthumous triumph for Sherman Kent. In some other fields, numbers have become standard. “Slight chance of showers” has given way to “30% chance of showers” in weather forecasts. But hopelessly vague language is still so common, particularly in the media, that we rarely notice how vacuous it is. It just slips by.