Iq changes across the lifespan
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Age-Related Changes in IQ Across the Lifespan
Research shows that IQ scores and cognitive abilities change in predictable ways as people age. In adulthood, there is a general pattern of decline in Full-Scale IQ (FSIQ) and specific cognitive domains such as verbal comprehension, perceptual reasoning, working memory, and processing speed. These declines are considered normal and can be tracked using standardized tests like the Wechsler Adult Intelligence Scales, which help distinguish between typical aging and unusual cognitive deterioration that may need further evaluation 14.
Stability and Variability of IQ Over Time
Despite the average decline in certain cognitive abilities with age, individual IQ scores tend to be highly stable across the lifespan. Large-scale longitudinal studies have found that a significant portion of a person's intelligence in old age can be predicted by their childhood IQ. For example, about 45% of the variance in intelligence at age 90 can be explained by intelligence at age 11, and similar stability has been observed from early adulthood into later life 34. However, some individuals do experience meaningful increases or decreases in IQ, especially during childhood and adolescence, and these changes are linked to brain development, particularly changes in cortical thickness .
Heritability and Environmental Influences on IQ
The heritability of IQ increases with age, reaching a high point in late adolescence and remaining stable into adulthood. By ages 18–20, genetic factors account for about 80% of the variation in IQ, while the influence of shared environment drops to about 10% . This means that as people grow older, their IQ is more strongly influenced by genetics and less by their shared family environment.
The Flynn Effect: Generational IQ Changes
IQ scores have generally increased over the past century, a phenomenon known as the Flynn Effect. Meta-analyses show that IQ gains have been stronger in younger generations and in middle-income countries, with an average increase of about 0.22 points per year globally 56. However, these gains are not uniform across all ages or ability levels. For example, in US adolescents, IQ gains were seen at age 13 but not at age 18, and those with lower ability levels actually showed declines over time . The Flynn Effect is also stronger for adults than for children and has slowed in recent decades .
Education and Cognitive Aging
Education is associated with higher IQ scores in later life, especially for those with lower initial IQs. However, more years of education do not appear to improve basic cognitive processing speed, which is another aspect of cognitive aging . This suggests that while education can enhance certain cognitive capacities, it may not slow all aspects of cognitive decline.
Childhood IQ and Long-Term Outcomes
Higher IQ in childhood is linked to better health and longer life. Studies tracking individuals from childhood into old age have found that those with higher IQs at age 11 have a lower risk of death and better health outcomes throughout life. This relationship is consistent across both men and women and is especially strong for deaths occurring before age 65 310.
Conclusion
IQ changes across the lifespan are shaped by a combination of genetic, environmental, and societal factors. While average cognitive abilities decline with age, individual IQ scores remain relatively stable, and early-life intelligence is a strong predictor of later-life outcomes. Generational trends like the Flynn Effect show that IQ can increase over time, but these gains are not uniform across all groups. Education and early cognitive ability play important roles in shaping cognitive health and longevity.
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