Review of Philip E. Tetlock, Expert political judgment: How good is it? How can we know?

Adrian E. Tschoegl, University of Pennsylvania
J. Scott Armstrong, University of Pennsylvania

Article comments

Postprint version. Published in International Journal of Forecasting, Volume 23, Issue 2, 2007, pages 339-342.
Publisher URL: http://dx.doi.org/10.1016/j.ijforecast.2007.02.002

Abstract

The book assaults common sense with evidence. In order to mount his assault on accepted wisdom, Tetlock spends some 238 pages of text explaining his methods and findings, and considering and refuting many alternative explanations, and adds some 75 pages of technical appendices. The downside of this approach is that some readers may find the book too demanding. That would be a pity as his findings are important.

Tetlock’s book reports the results of a two-decade long study of expert predictions. He recruited 284 people whose professions included "commenting or offering advice on political and economic trends." He asked them to forecast the probability that various situations would or would not occur, picking areas (geographic and substantive) within and outside their areas of expertise. In addition to eliciting forecasts, Tetlock also asked questions aimed at understanding how the forecasters came to formulate their forecasts, how they dealt with the failure of their forecasts, how they responded to contradictory information, and how they evaluated the probable accuracy of others' theories and predictions. By 2003, he had accumulated 82,361 forecasts, which provided him a database to evaluate. He then evaluated experts' predictions against outcomes, and against various alternate predictions that he derived from simple statistical procedures, from uninformed non-experts, and from well-informed non-experts.