Facts about IQ

1. 11

   Reaction time tasks show correlations of 0.3 to 0.4 with IQ scores, with faster neural processing speeds in high-IQ individuals measurable through millisecond-level response variations.

   IQMay 14sharemeasurementneurosciencecognition
2. 10

   Adopted children show IQ correlations of 0.2 to 0.3 with biological parents they've never met, but 0.3 to 0.4 with adoptive parents they were raised by, demonstrating environmental influence on test performance.

   IQMay 14shareenvironmentadoptiongenetics
3. 09

   Testing for cognitive ability began formally in 1905 when Alfred Binet and Théodore Simon created the first intelligence scale to identify Parisian children needing educational support.

   IQMay 14sharehistorymeasurementpsychology
4. 08

   Socioeconomic status accounts for approximately 25 to 30 percent of IQ variation between individuals, with environmental factors like nutrition, education quality, and stress playing measurable roles in test performance.

   IQMay 14shareenvironmentsocioeconomicvariation
5. 07

   Standardized IQ tests demonstrate a strong correlation with academic performance and job outcomes, with correlations of 0.5 to 0.7 for educational achievement and 0.3 to 0.5 for workplace success across diverse professions.

   IQMay 14sharemeasurementpsychologyprediction
6. 06

   Women and men show negligible differences in average IQ scores, with meta-analyses across decades finding gaps of fewer than three points, contradicting historical claims of cognitive superiority.

   IQMay 14sharegenderpsychologymeasurement
7. 05

   Brain size correlates with IQ at approximately 0.4, a moderate relationship suggesting neurological efficiency matters more than absolute head dimensions.

   IQMay 14shareneurosciencemeasurementbiology
8. 04

   Approximately 2 to 3 percent of the population scores above 130 on IQ tests, qualifying as exceptionally gifted by most psychological standards.

   IQMay 14sharemeasurementpsychologystatistics
9. 03

   Crystallized intelligence, measured by vocabulary and accumulated knowledge, typically increases until age 60, while fluid intelligence, tested through pattern recognition and novel problem-solving, peaks around age 25.

   IQMay 14shareagingmeasurementcognition
10. 02

    Heritability estimates for IQ range from 50 to 80 percent in developed countries, meaning genetics accounts for roughly half to three-quarters of variation between individuals.

    IQMay 14sharegeneticsmeasurementpsychology
11. 01

    The Flynn effect documented a steady increase of approximately three IQ points per decade throughout the twentieth century in developed nations.

    IQMay 14sharemeasurementpsychologyhistory