A Meta-Analysis of Research on Hindsight Bias

We conducted a meta-analysis of research on hindsight bias to gain an up-to-date summary of the overall strength of hindsight effects and to test hypotheses about potential moderators of hindsight distortion. A total of 95 studies (83 published and 12 unpublished) were included, and 252 independent effect sizes were coded for moderator variables in 3 broad categories involving characteristics of the study, of measurement, and of the experimental manipulation. When excluding missing effect sizes, the overall mean effect size was Md = .39 with a 95% confidence interval of .36 to .42. Five main findings emerged: (a) effect sizes calculated from objective probability estimates were larger than effect sizes calculated from subjective probability estimates; (b) effect sizes of studies that used almanac questions were larger than effect sizes of studies that used real-world events or case histories; (c) studies that included neutral outcomes resulted in larger effect sizes than studies that used positive or negative outcomes; (d) studies that included manipulations to increase hindsight bias resulted in significantly larger effect sizes than studies in which there were no manipulations to reduce or increase hindsight bias; and (e) studies that included manipulations to reduce hindsight bias did not produce lower effect sizes. These findings contribute to our understanding of hindsight bias by updating the state of knowledge, widening the range of known moderator variables, identifying factors that may activate different mediating processes, and highlighting critical gaps in the research literature.