iq levels by age

Introduction

The relationship between IQ levels and age has been a subject of extensive research. Various studies have explored how IQ changes over the lifespan, the factors influencing these changes, and the implications of IQ at different ages. This synthesis aims to present a cohesive understanding of the findings from multiple research papers on this topic.

Key Insights

IQ Stability and Predictability in Early Childhood:
- IQ scores in young children, particularly those assessed at ages 2 to 3, 4 to 5, and 6 to 7, show stability and can predict later IQ scores, especially when the same test is used at both assessments.
- The Ages & Stages Questionnaire (ASQ) at 36 months can predict IQ at ages 5 to 6, with maternal education level being a significant factor.
IQ Changes Across Adulthood:
- Performance IQ and Full Scale IQ decline with age from 20 to 74 years, even when educational attainment is controlled. However, Verbal IQ remains stable across this age range.
- The heritability of IQ increases with age, reaching an asymptote at about 0.80 at 18-20 years and continuing at that level into adulthood, while shared environmental influence decreases.
Impact of Childhood IQ on Later Life Outcomes:
- Higher childhood IQ is associated with lower risk of all-cause mortality, with a stronger effect observed in deaths occurring before age 65 compared to those occurring after age 65 .
Age-Related Variability in IQ:
- Older adults (aged 60-79) show increased variability in timing tasks related to IQ, although their average performance remains accurate.
- The Flynn Effect, which describes generational increases in IQ, shows significant variability by age and ability level, with some age groups (e.g., 18-year-olds) experiencing a decline in IQ over time.
Sex Differences in IQ:
- Longitudinal studies indicate that girls have a slight IQ advantage at ages 7 and 11, but by age 16, boys show a higher average IQ.

Conclusion

Research indicates that IQ levels exhibit both stability and change across different stages of life. In early childhood, IQ scores are relatively stable and predictive of future IQ. In adulthood, while Verbal IQ remains stable, Performance IQ and Full Scale IQ tend to decline. The heritability of IQ increases with age, and higher childhood IQ is linked to lower mortality risk, particularly before age 65. Additionally, the Flynn Effect varies by age and ability level, and sex differences in IQ become apparent during adolescence. These findings collectively highlight the complex interplay between age, IQ, and various influencing factors.

Summary

Introduction

Key Insights

Conclusion

Sources and full results

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.

Childhood IQ and survival to 79: Follow-up of 94% of the Scottish Mental Survey 1947

Higher childhood IQ is associated with lower risk of all-cause mortality in both men and women, with a slightly stronger effect in women and before age 65.

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.

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.

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.

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.

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

The Flynn Effect for fluid IQ may not apply to all ages or ability levels, with lower ability levels experiencing worsening IQ over time.

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.

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.

Age and intelligence of a group of juvenile delinquents

Boys aged 14 and over have a slightly higher mean IQ than those below 14 years, but no significant differences were found between sexes.

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