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The problem
Intervention: No intervention tested; this is an observational study examining natural variation in early-life stature, child IQ, and schooling and their association with adult cognitive outcomes
Who it was tested with: 2,614 individuals from four birth cohorts: Brazil (born 1993), Guatemala (born 1969-77), Philippines (born 1983-84), and South Africa (born 1990).
Children or communities are compared with a group that did not receive the intervention, or followed over years. This is the design that best separates what the intervention did from everything else that changed.
"Using multivariable linear models, we estimated the relative contributions of early-life stature, child IQ, and schooling (highest school year completed) to adult IQ, including interaction effects among the early-childhood measures and schooling." The study employed prospective longitudinal data with repeated cognitive measurements and statistical controls to disentangle the relative importance of early growth versus early cognitive ability in predicting adult intelligence.
This is an observational study without experimental manipulation, so causality cannot be inferred. Cohort effects, differences in measurement protocols across sites, and unmeasured confounders may affect results. Heterogeneity across cohorts limits generalisation.
Across countries and designs
18 studies · 28 countries
