iq age chart

Introduction

The relationship between age and IQ has been a subject of extensive research, with various studies examining how IQ changes over the lifespan, the heritability of IQ, and the factors influencing these changes. This synthesis aims to present key insights from multiple research papers on the topic of IQ and age.

Key Insights

Heritability of IQ Increases with Age:
- The heritability of IQ increases with age, reaching an asymptote of about 0.80 at 18-20 years and continuing at that level into adulthood. Shared environmental influences decrease across age, approximating about 0.10 at 18-20 years and continuing at that level into adulthood.
Childhood IQ and Mortality:
- Childhood IQ is significantly related to mortality risk up to age 65, with a 36% increased risk per standard deviation decrease in childhood IQ. This relationship is attenuated after adjusting for socio-economic factors. There is no significant relationship between childhood IQ and mortality risk after age 65.
Predictive Value of Early IQ Assessments:
- The Ages & Stages Questionnaire (ASQ) at 36 months can predict IQ at 5-6 years, with maternal education level being a significant factor associated with lower IQ in preschool children.
- IQ scores in young autistic children are stable and predictive of later IQ, especially when the same test is used at both assessments and when children are 4 years or older at initial assessment.
Age-Related Changes in IQ:
- IQ scores, particularly Performance IQ and Full Scale IQ, decline with age from 20 to 74 years, even after controlling for educational attainment. Verbal IQ, however, does not show a significant decline when education is controlled.
- Older adults (60-79 years) show increased variability in timing tasks related to IQ, although they can still perform these tasks accurately on average.
Impact of Early Intervention on IQ:
- Higher IQ at intake and younger age are predictive of better educational placement outcomes for children with autism. Early intervention is crucial for improving IQ and educational outcomes.
Sex Differences in IQ:
- At ages 7 and 11, girls have a slight IQ advantage over boys, but by age 16, boys have a slight IQ advantage over girls.

Conclusion

The research indicates that IQ is influenced by a variety of factors across the lifespan. Heritability of IQ increases with age, while shared environmental influences decrease. Early childhood IQ is a significant predictor of later outcomes, including mortality risk and educational placement, particularly in special populations like autistic children. Age-related declines in IQ are evident, especially in performance-related tasks, and early intervention can significantly impact IQ outcomes. Additionally, there are slight sex differences in IQ that change with age. Overall, these findings highlight the complex interplay between age, IQ, and various influencing factors.

Summary

Introduction

Key Insights

Conclusion

Sources and full results

The Wilson Effect: The Increase in Heritability of IQ With Age

The heritability of IQ increases with age, reaching an asymptote of 0.80 at 18-20 years of age and continuing at that level well into adulthood, while shared environmental influence decreases across age.

Childhood IQ and all-cause mortality before and after age 65: prospective observational study linking the Scottish Mental Survey 1932 and the Midspan studies.

Childhood IQ is significantly related to deaths before age 65, but not to deaths after age 65.

Ages and Stages Questionnaire at 3 Years for Predicting IQ at 5–6 Years

The 36-month Ages & Stages Questionnaire (ASQ) score at 36 months can effectively predict IQ at age 5-6 years, with low maternal education level being a major risk factor for lower IQ in preschool children.

A classical IQ model of the stages of cognitive development

The classical IQ model accurately predicts cognitive development stages in individuals aged 13-17 years, highlighting the importance of general cognitive capacity in differential psychology.

Age and WAIS-R intelligence in a national sample of adults in the 20- to 74-year age range: A cross-sectional analysis with educational level controlled

Intelligence declines in Performance IQ and Full Scale IQ from age 20 to 74, but not in Verbal IQ, even after controlling for education.

The role of age at assessment, developmental level, and test in the stability of intelligence scores in young autistic children

Intelligence scores in young autistic children are more stable and predictable when used at both initial and reassessment, and when children are 4 years or older.

Age and IQ effects on stimulus and response timing

Increased age and decreasing IQ tend to increase variability in judgments of duration, but overall accuracy in timing tasks remains generally consistent across groups.

Age and IQ at Intake as Predictors of Placement for Young Children with Autism: A Four- to Six-Year Follow-Up

Higher IQ and younger age predict regular education placement for children with autism, while lower IQ and older age are linked to special education placement.

Age Differences within Secular IQ Trends: An Individual Growth Modeling Approach.

The relationship between IQ and age is complex, with older children experiencing smaller declines in test scores when new norms replace older ones, but these differences disappear in current testing.

A longitudinal study of sex differences in intelligence at ages 7, 11 and 16 years

At age 16, boys have an IQ advantage of 1.8 IQ points over girls, supporting Lynn's hypothesis that males develop higher average intelligence than females.

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