“Of Differing Methods, Disputed Estimates and Discordant Interpretations: the Meta-Analytical Multiverse of Brain Volume and IQ Associations”, Jakob Pietschnig, Daniel Gerdesmann, Michael Zeiler, Martin Voracek2022-05-11 (IQ, neuroscience)⁠:

Brain size and IQ are positively correlated. However, multiple meta-analyses have led to considerable differences in summary effect estimations, thus failing to provide a plausible effect estimate.

Here we aim at resolving this issue by providing the largest meta-analysis and systematic review so far of the brain volume and IQ association (86 studies; 454 effect sizes from k = 194 independent samples; n > 26,000) in 3 cognitive ability domains (full-scale, verbal, performance IQ).

By means of competing meta-analytical approaches as well as combinatorial and specification curve analyses, we show that most reasonable estimates for the brain size and IQ link yield r-values in the mid-0.20s, with the most extreme specifications yielding rs of 0.10 and 0.37.

Summary effects appeared to be somewhat inflated due to selective reporting, and cross-temporally decreasing effect sizes indicated a confounding decline effect, with 3⁄4^th of the summary effect estimations according to any reasonable specification not exceeding r = 0.26, thus contrasting effect sizes were observed in some prior related, but individual, meta-analytical specifications. Brain size and IQ associations yielded r = 0.24, with the strongest effects observed for more g-loaded tests and in healthy samples that generalize across participant sex and age bands.

[Keywords: multiverse analysis, in vivo brain volume, systematic review, intelligence, specification curve analysis, meta-analysis]

See Also:

• Genome-wide meta-analysis of brain volume identifies genomic loci and genes shared with intelligence

• The causal influence of brain size on human intelligence: Evidence from within-family phenotypic associations and GWAS modeling

• Structural brain imaging correlates of general intelligence in UK Biobank

• A Polygenic Score for Higher Educational Attainment is Associated With Larger Brains

• A combined analysis of genetically correlated traits identifies 187 loci and a role for neurogenesis and myelination in intelligence

• Are Bigger Brains Smarter? Evidence From a Large-Scale Preregistered Study

• The Dynamic Associations Between Cortical Thickness and General Intelligence are Genetically Mediated

• Linking Brain Biology to Intellectual Endowment: A Review on the Associations of Human Intelligence With Neuroimaging Data

• Reproducible brain-wide association studies require thousands of individuals