Flynn effect

The Flynn effect is the substantial rise in average IQ test scores observed across generations during much of the twentieth century, especially on tests of abstract reasoning.

Fluid and crystallized intelligence: Fluid intelligence is reasoning in unfamiliar situations; crystallized intelligence is knowledge and skills acquired through experience. Gains have often been larger on tests of abstract reasoning than on tests of acquired knowledge.
Raven's Progressive Matrices: A set of nonverbal tests that assess pattern completion and abstract reasoning. Large gains on these tests helped draw attention to rising performance on abstract reasoning tasks.
Regression to the mean: The statistical tendency for unusually high or low measurements to be less extreme on repetition. It explains some changes across repeated measurements, but not persistent cohort gains across whole populations.
IQ test norming: The process of setting test score scales using performance data from a reference population. Tests are periodically renormed because raw performance gains would otherwise inflate reported IQ scores.
Nutrition and intelligence: The study of how diet and nutritional status relate to cognitive development and performance. Improved childhood nutrition is one proposed contributor to rising test scores.
James R. Flynn: A political scientist whose analyses of historical IQ data brought the generational score gains to prominence. His cross-national comparisons established the pattern now bearing his name.
Measurement invariance: The condition that a measurement instrument assesses the same construct in comparable ways across groups or time. Comparisons across generations depend on whether IQ tests retain comparable meaning over time.
Standardized testing: Assessment using consistent procedures and scoring rules to compare performance across people or groups. The effect highlights how comparisons depend on the tests and reference populations used.
Education and intelligence: The study of how education relates to cognitive abilities and measured intelligence. Expanded schooling may strengthen the abstract reasoning skills measured by many IQ tests.
United States intelligence testing: The development and use of standardized intelligence tests in the United States. Long-running American test records provided evidence of rising scores across birth cohorts.

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