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Cited by 32Cognitive Abilities and TestingIntergenerational and Educational Inequality StudiesDown syndrome and intellectual disability research

The Flynn effect for fluid IQ may not generalize to all ages or ability levels: A population-based study of 10,000 US adolescents

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Platt, Jonathan M., Keyes, Katherine M., McLaughlin, Katie A., Kaufman, Alan S.·2019·Intelligence
DOI 10.1016/j.intell.2019.101385PMC PMC7176308
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Abstract

Generational changes in IQ (the Flynn Effect) have been extensively researched and debated. Within the US, gains of 3 points per decade have been accepted as consistent across age and ability level, suggesting that tests with outdated norms yield spuriously high IQs. However, findings are generally based on small samples, have not been validated across ability levels, and conflict with reverse effects recently identified in Scandinavia and other countries. Using a well-validated measure of fluid intelligence, we investigated the Flynn Effect by comparing scores normed in 1989 and 2003, among a representative sample of American adolescents ages 13-18 (n=10,073). Additionally, we examined Flynn Effect variation by age, sex, ability level, parental age, and SES. Adjusted mean IQ differences per decade were calculated using generalized linear models. Overall the Flynn Effect was not significant; however, effects varied substantially by age and ability level. IQs increased 2.3 points at age 13 (95% CI=2.0, 2.7), but decreased 1.6 points at age 18 (95% CI=-2.1, -1.2). IQs decreased 4.9 points for those with IQ<70 (95% CI=-4.9, -4.8), but increased 3.5 points among those with IQ>130 (95% CI=3.4, 3.6). The Flynn Effect was not meaningfully related to other background variables. Using the largest sample of US adolescent IQs to date, we demonstrate significant heterogeneity in fluid IQ changes over time. Reverse Flynn Effects at age 18 are consistent with previous data, and those with lower ability levels are exhibiting worsening IQ over time. Findings by age and ability level challenge generalizing IQ trends throughout the general population.

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  • Platt et al. (2019) observed Flynn effects by age: age 13 (+2.33), age 14 (+0.88), age 15 (−0.89), age 16 (−0.19), age 17 (−0.76), and age 18 (−1.66).

    “Platt et al. (2019) observed the following Flynn effects for each separate age group in their large-scale investigation: age 13 (+2.33), age 14 (+0.88), age 15 (−0.89), age 16 (−0.19), age 17 (−0.76), and age 18 (−1.66).”

    From Wait, Where’s the Flynn Effect on the WAIS-5? (2024) · cites this paper as Platt et al. 2019

    The Results (page unavailable) report an increase of about 2.3 IQ points per decade at age 13 and a decrease of about 1.6 at age 18, broadly supporting the quoted endpoints. The passages available from our copy do not give the exact estimates for ages 14–17; moreover, the quoted change from −0.89 at 15 to −0.19 at 16 does not follow the Results’ description of a monotonic decrease with age. (LLM, conf=0.85)

    Experimental — accuracy not yet measured

  • Platt et al. (2019) observed a significant interaction between age and the Flynn effect for more than 10,000 adolescents ages 13-18 on a test of fluid reasoning.

    “The significant and striking interaction between age and the Flynn effect reported for 10,000+ adolescents ages 13–18 on a test of fluid reasoning (Platt et al. 2019) underscores the need to avoid generalizing the findings to any child or adolescent below age 16.”

    From Wait, Where’s the Flynn Effect on the WAIS-5? (2024) · cites this paper as Platt et al. 2019

    The Abstract reports 10,073 adolescents ages 13–18 tested with a measure of fluid intelligence, and the Results report substantial variation in the Flynn effect by age. However, Materials and Methods (Analysis) explicitly says the authors did not test for additive statistical interaction, so describing the age interaction as statistically significant goes beyond what the paper establishes. Page numbers were not available in our copy. (LLM, conf=0.88)

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Authors
Platt, J. M., Keyes, K. M., McLaughlin, K. A., & Kaufman, A. S.
Affiliations
  • Columbia University (US)
  • Universidad Mayor (CL)
  • Harvard University (US)
  • Yale University (US)
Corresponding author
Platt, Jonathan M.
ORCID
Venue
Intelligence
Publisher
Elsevier BV
Published
2019-11
Volume
77
Pages
101385
ISSN
0160-2896 (ISSN-L)
DOI
10.1016/j.intell.2019.101385
PMC
PMC7176308
OpenAlex
W2972529659
Cited by
32
References
4
Citations by year
2026: 1 · 2025: 2 · 2024: 7 · 2023: 4 · 2022: 5 · 2021: 11 · 2020: 1 · 2013: 1
FWCI
4.73
Type
journal article
Language
en
Open access
Licence
Locations
  • Intelligence (publishedVersion)
  • PubMed (publishedVersion)
  • PubMed Central (acceptedVersion)
  • RePEc: Research Papers in Economics (submittedVersion)
Funders
  • National Institutes of Health
  • Jacobs Foundation
Topics
  • Social Sciences › Psychology › Experimental and Cognitive Psychology › Cognitive Abilities and Testing
  • Social Sciences › Sociology and Political Science › Intergenerational and Educational Inequality Studies
  • Health Sciences › Medicine › Public Health, Environmental and Occupational Health › Down syndrome and intellectual disability research
Keywords
Flynn effect, fluid intelligence, IQ trends, adolescents, ability level differences, socioeconomic status, parental age, sex differences

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