Reference class forecasting predicts the outcome of a planned action based on actual outcomes in a reference class of similar actions to that being forecast. The theories behind reference class forecasting were developed by Daniel Kahneman and Amos Tversky. The methodology and data needed for employing reference class forecasting in practice in policy, planning, and management were developed by Oxford professor Bent Flyvbjerg and the COWI consulting group in a joint effort. The theoretical work helped Kahneman win the Nobel Prize in Economics. Today, reference class forecasting has found widespread use in practice in both public and private sector policy and management.
source: http://en.wikipedia.org/wiki/Reference_class_forecasting