On the reality of cognitive illusions

The study of heuristics and biases in judgment has been criticized in several publications by G. Gigerenzer, who argues that "biases are not biases" and "heuristics are meant to explain what does not exist" (1991, p. 102). This article responds to Gigerenzer's critique and shows that it misrepresents the authors' theoretical position and ignores critical evidence. Contrary to Gigerenzer's central empirical claim, judgments of frequency—not only subjective probabilities—are susceptible to large and systematic biases. A postscript responds to Gigerenzer's (1996) reply.