Does iq vary with age

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The Relationship Between IQ and Age: A Comprehensive Analysis

Heritability of IQ and Age

Increasing Heritability with Age

Research has shown that the heritability of IQ increases with age, a phenomenon known as the "Wilson Effect." Studies involving twins and adoption cases indicate that the heritability of IQ reaches approximately 0.80 by the age of 18-20 and remains at that level into adulthood. Concurrently, the influence of shared environmental factors decreases to about 0.10 by the same age range and continues at that level into adulthood.

Genetic Contributions to IQ Stability

Genetic factors play a significant role in the stability and change of intelligence from childhood to old age. A study using genome-wide single nucleotide polymorphism (SNP) data estimated that genetic variants account for 24% of the variation in cognitive ability changes from childhood to old age. The genetic correlation between intelligence at age 11 and in old age was found to be 0.62, indicating a substantial genetic contribution to IQ stability over a lifetime.

Age-Related Changes in IQ

Decline in Cognitive Performance with Age

Aging impacts cognitive performance, particularly in tasks requiring quick decision-making and memory. Studies have shown that older adults (aged 60-90) exhibit declines in performance on tasks such as numerosity discrimination, recognition memory, and lexical decision. However, these declines are not significantly different between individuals with high and low IQs, suggesting that while age affects cognitive performance, the impact is relatively uniform across different IQ levels.

Variability in IQ Changes Over Time

Longitudinal studies have demonstrated that IQ stability varies over time and is influenced by the initial level of IQ. For instance, children with higher initial IQ scores tend to maintain their advantage into early adulthood, while those with lower initial IQ scores show higher stability over time. This indicates that while IQ can change, the degree of change is moderated by the initial IQ level.

The Flynn Effect and Age

Generational Changes in IQ

The Flynn Effect, which describes generational increases in IQ scores, does not apply uniformly across all ages and ability levels. A study of 10,000 US adolescents found that while IQs increased by 2.3 points at age 13, they decreased by 1.6 points at age 18. Additionally, IQs decreased significantly for those with lower initial IQs but increased for those with higher initial IQs. This suggests that generational IQ changes are heterogeneous and vary significantly by age and ability level.

Impact of Early IQ on Later Life

Long-Term Stability and Health Outcomes

Longitudinal data from the Scottish Mental Surveys of 1932 and 1947 indicate that IQ differences observed in childhood are stable across the lifespan. Higher childhood IQ is associated with lower mortality and better health outcomes in old age. This stability underscores the long-term impact of early cognitive abilities on later life outcomes.

Sex Differences in IQ Development

A longitudinal study examining sex differences in IQ found that girls initially have a slight IQ advantage at ages 7 and 11. However, by age 16, boys exhibit a higher average IQ than girls. This shift suggests that sex differences in IQ can change over time, potentially influenced by developmental and environmental factors.

Conclusion

In summary, IQ varies with age due to a combination of genetic, environmental, and developmental factors. Heritability of IQ increases with age, while shared environmental influences decrease. Cognitive performance declines with age, but the impact is consistent across different IQ levels. The Flynn Effect shows that generational changes in IQ are not uniform across all ages and ability levels. Early IQ has a lasting impact on later life outcomes, including health and mortality, and sex differences in IQ can evolve over time. Understanding these dynamics is crucial for developing strategies to support cognitive health across the lifespan.