Why did intelligence test scores rise throughout the 20th century?

The Flynn effect is the substantial and long-sustained increase in intelligence test scores observed across many parts of the world throughout the 20th century. Named after researcher James Flynn, this phenomenon shows that when contemporary populations take older standardized tests, their average scores are significantly above the baseline of 100. While proposed explanations include improvements in education and nutrition, some researchers have noted potential recent reversals in developed nations.

What we know

• The Flynn effect describes a substantial and long-sustained increase in both fluid and crystallized intelligence test scores measured over the 20th century. [2]
• When test subjects from later generations take older standardized IQ tests, their average scores are almost always significantly above 100. [2]
• Raw scores on intelligence quotient tests for many populations have risen at an average rate of about three points per decade since the early 20th century. [4]
• Proposed explanations for these score increases include the rising efficiency and availability of education. [2] · medium confidence

Still open

• Some researchers suggest a mild reversal or decline in IQ scores in developed countries beginning in the 1990s, while meta-analyses up to the mid-2010s indicate the overall Flynn effect has continued at a similar or slower rate.

Where to go next

• whoWho was James Flynn?
• how it workedHow are modern IQ tests standardized?
• what followedCould intelligence test scores be declining now?
• the bigger pictureHow do national IQ comparisons relate to economic prosperity?
• how we knowHow did British children score on Raven's matrices over time?
• an unexpected connectionHow does moral philosophy connect to intelligence research?James Flynn, the researcher who discovered the multi-decade rise in IQ scores, was professionally trained and worked primarily as a moral philosopher rather than a traditional psychometrician.

Sources

• [1]Flynn effect (Wikidata Q508736) · CC0 1.0
• [2]Flynn effect · CC BY-SA 4.0
• [3]James Flynn (academic) · CC BY-SA 4.0
• [4]Intelligence quotient · CC BY-SA 4.0
• [5]Nations and IQ · CC BY-SA 4.0