In this meta-study, we analyzed 2,442 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 in this multidisciplinary field. We found that the average effect size in intelligence research was a Pearson’s correlation of .26, and the median sample size was 60. We estimated the power of each primary study by using the corresponding meta-analytic effect as a proxy for the true effect. The median estimated power across all studies was 51.7%, with only 31.7% of the studies reaching a power of 80% or higher. We documented differences in average effect size and median estimated power between different types of in intelligence studies (correlational studies, studies of group differences, experiments, toxicology, and behavior genetics). Across all meta-analyses, we found evidence for small study effects, potentially indicating publication bias and overestimated effects. We found no differences in small study effects between different study types. We also found no convincing evidence for the decline effect, US effect, or citation bias across meta-analyses. We conclude that intelligence research does show signs of low power and publication bias, but that these problems seem less severe than in many other scientific fields.
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