Normal iq levels by age

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Normal IQ Levels by Age

Childhood IQ Levels and Predictive Validity

Early Childhood IQ Stability

Research indicates that IQ levels in children between the ages of 3 and 18 can be used to predict future educational and occupational status. By the second grade, these predictive correlations are similar to those found in adults, particularly concerning occupational status. However, these correlations are not strong enough for long-term predictions for individual children .

Impact of Phenylketonuria (PKU) on IQ

Studies on children treated early for phenylketonuria (PKU) show that IQ development stabilizes after the age of 10, regardless of dietary relaxation. Children with lower blood phenylalanine levels in early and middle childhood tend to have near-normal IQ outcomes. This suggests that PKU can suppress overall IQ without affecting specific cognitive domains.

Adolescent IQ Trends

The Flynn Effect in Adolescents

The Flynn Effect, which describes generational IQ gains, shows variability among adolescents. A study of 10,000 US adolescents aged 13-18 found that IQs increased by 2.3 points at age 13 but decreased by 1.6 points at age 18. This effect also varied by ability level, with lower IQ individuals showing a decline and higher IQ individuals showing an increase over time.

Adult IQ Levels

IQ Stability in Adults with Autism

For adults with autism who had average IQs as children, IQ levels generally remain stable into mid-to-late adulthood. However, a significant minority of these individuals experience severe behavioral issues and cognitive decline, often associated with epilepsy and severe language impairments.

Heritability of IQ in Adulthood

The heritability of IQ increases with age, reaching an asymptote of about 0.80 by the age of 18-20 and maintaining this level into adulthood. Shared environmental influences decrease significantly by this age, suggesting that genetic factors play a more substantial role in adult IQ.

IQ Norms for Highly Intelligent Adults

Normative data for highly intelligent adults (IQ ≥ 120) show that cognitive performance remains stable over time. This data helps clinicians identify typical cognitive performance and detect abnormal cognitive decline in individuals at risk for dementia.

Aging and IQ

Brain Aging and IQ Stability

In older adults, brain anatomical measures such as grey matter and white matter volumes decrease with age, while lateral ventricle volumes and white matter hypointensities increase. Despite these neuroanatomical changes, verbal and non-verbal IQ measures remain stable over time, indicating that cognitive decline is not necessarily linked to brain volume changes in healthy older adults.

Conclusion

IQ levels exhibit varying degrees of stability and change across different age groups. Childhood IQ can predict future outcomes to some extent, while adolescent IQ trends show generational variability. In adulthood, IQ remains relatively stable, with genetic factors playing a significant role. Despite age-related brain changes, cognitive abilities in older adults can remain stable, highlighting the complex relationship between brain anatomy and intelligence.