At what age does your iq stop increasing
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Age and IQ Development: When Does IQ Stop Increasing?
Heritability of IQ and Age: The Wilson Effect
Research has shown that the heritability of IQ increases with age, a phenomenon known as the Wilson Effect. Studies indicate that the heritability of IQ reaches an asymptote at about 0.80 between the ages of 18 and 20, and this level of heritability continues well into adulthood. This suggests that genetic factors play a more significant role in determining IQ as individuals grow older, while the influence of shared environmental factors decreases to about 0.10 by the same age range.
Stability of IQ in Phenylketonuria Patients
Longitudinal studies on patients with phenylketonuria (PKU) reveal that IQ development stabilizes after the age of 10, regardless of dietary relaxation. This stability suggests that, at least for individuals with PKU, significant changes in IQ are unlikely to occur after this age. However, it is important to note that these findings are specific to PKU patients, and there is a lack of research on IQ development in these individuals during middle or late adulthood.
Cognitive Reserve and Terminal Decline
The cognitive reserve hypothesis posits that individuals with higher IQs can better tolerate age-related brain pathologies, delaying the onset of terminal decline (TD) in cognitive abilities. Data from a study following individuals from age 70 until death showed that higher IQs were associated with a delayed onset of TD by approximately 1.87 years for perceptual and motor speed and 1.96 years for verbal ability. However, once TD begins, the rate of decline is steeper for those with higher IQs. This indicates that while higher IQ can delay cognitive decline, it does not prevent it entirely.
The Flynn Effect and Age Variability
The Flynn Effect, which describes generational increases in IQ scores, does not generalize uniformly across all ages. A study involving 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. This variability suggests that IQ changes over time are not consistent across different age groups, challenging the notion that IQ trends can be generalized throughout the entire population.
Conclusion
In summary, the heritability of IQ stabilizes around the ages of 18 to 20, and significant changes in IQ are unlikely to occur after this period. For specific populations, such as PKU patients, IQ stabilizes even earlier, around age 10. While higher IQ can delay the onset of cognitive decline in old age, it does not prevent it. Additionally, the Flynn Effect shows that IQ changes over time are not uniform across all age groups, indicating that age-specific factors play a crucial role in IQ development.
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