title: Empirical assessment of published effect sizes and power in the recent cognitive neuroscience and psychology literature.
abstract: We have empirically assessed the distribution of published effect sizes and estimated power by analyzing 26,841 statistical records from 3,801 cognitive neuroscience and psychology papers published recently. The reported median effect size was D = 0.93 (interquartile range: 0.64-1.46) for nominally statistically significant results and D = 0.24 (0.11-0.42) for nonsignificant results. Median power to detect small, medium, and large effects was 0.12, 0.44, and 0.73, reflecting no improvement through the past half-century. This is so because sample sizes have remained small. Assuming similar true effect sizes in both disciplines, power was lower in cognitive neuroscience than in psychology. Journal impact factors negatively correlated with power. Assuming a realistic range of prior probabilities for null hypotheses, false report probability is likely to exceed 50% for the whole literature. In light of our findings, the recently reported low replication success in psychology is realistic, and worse performance may be expected for cognitive neuroscience.
authors.affiliation: Department of Psychology, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Denes
authors.initials: D
authors.lastname: Szucs
authors.affiliation: Meta-Research Innovation Center at Stanford (METRICS) and Department of Medicine, Department of Health Research and Policy, and Department of Statistics, Stanford University, Stanford, California, United States of America.
authors.forename: John P A
authors.initials: JP
authors.lastname: Ioannidis
mesh_terms: D000066494:Cognitive Neuroscience / Q000706:statistics & numerical data*; D036262:Empirical Research; D006801:Humans; D011336:Probability; D011584:Psychology / Q000706:statistics & numerical data*; D011642:Publications / Q000706:statistics & numerical data*; D011795:Surveys and Questionnaires