Flynn effect and its reversal are both environmentally caused
Population intelligence scores rose through the twentieth century, a phenomenon known as the Flynn effect, though recent years have seen a slowdown or reversal in several countries. The authors sort hypothesised causes by whether they allow for within-family Flynn effects. Using Norwegian register data and cognitive scores from military conscription covering three decades of birth cohorts, they show that the observed effect, its turning point and the later decline can all be recovered from within-family variation, which controls for all factors shared by siblings.
Population intelligence scores rose through the twentieth century, a phenomenon known as the Flynn effect, though recent years have seen a slowdown or reversal in several countries. The authors sort hypothesised causes by whether they allow for within-family Flynn effects. Using Norwegian register data and cognitive scores from military conscription covering three decades of birth cohorts, they show that the observed effect, its turning point and the later decline can all be recovered from within-family variation, which controls for all factors shared by siblings.
Written from the abstract as shown on the OpenAlex record, read 2026-11-04.
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RECORD-ONLY, published record verified but content NOT read: Bratsberg, B., & Rogeberg, O. (2018). Flynn effect and its reversal are both environmentally caused. PNAS, 115(26), 6674-6678. doi:10.1073/pnas.1718793115.