Journal of Intelligence Article Effect Sizes, Power, and Biases in Intelligence Research: A Meta-Meta-Analysis Michèle B. Nuijten 1,* , Marcel A. L. M. van Assen 1,2, Hilde E. M. Augusteijn 1, Elise A. V. Crompvoets 1 and Jelte M. Wicherts 1 1 Department of Methodology & Statistics, Tilburg School of Social and Behavioral Sciences, Tilburg University, Warandelaan 2, 5037 AB Tilburg, The Netherlands;
[email protected] (M.A.L.M.v.A.);
[email protected] (H.E.M.A.);
[email protected] (E.A.V.C.);
[email protected] (J.M.W.) 2 Section Sociology, Faculty of Social and Behavioral Sciences, Utrecht University, Heidelberglaan 1, 3584 CS Utrecht, The Netherlands * Correspondence:
[email protected]; Tel.: +31-13-466-2053 Received: 7 May 2020; Accepted: 24 September 2020; Published: 2 October 2020 Abstract: In this meta-study, we analyzed 2442 effect sizes from 131 meta-analyses in intelligence research, published from 1984 to 2014, to estimate the average effect size, median power, and evidence for bias. We found that the average effect size in intelligence research was a Pearson’s correlation of 0.26, and the median sample size was 60. Furthermore, across primary studies, we found a median power of 11.9% to detect a small effect, 54.5% to detect a medium effect, and 93.9% to detect a large effect. We documented differences in average effect size and median estimated power between different types of intelligence studies (correlational studies, studies of group differences, experiments, toxicology, and behavior genetics).