Superforecasting: The Art and Science of Prediction

by Philip E. Tetlock

When we make estimates, we tend to start with some number and adjust. The number we start with is called the anchor. It’s important because we typically underadjust, which means a bad anchor can easily produce a bad estimate. And it’s astonishingly easy to settle on a bad anchor. In classic experiments, Daniel Kahneman and Amos Tversky showed you could influence people’s judgment merely by exposing them to a number—any number, even one that is obviously meaningless, like one randomly selected by the spin of a wheel.10 So a forecaster who starts by diving into the inside view risks being swayed by a number that may have little or no meaning. But if she starts with the outside view, her analysis will begin with an anchor that is meaningful. And a better anchor is a distinct advantage.