Iq levels by age
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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
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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.
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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.
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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 .
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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.
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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.
Sources and full results
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