Does iq score change with age
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Changes in IQ Scores with Age: A Comprehensive Analysis
Decline in IQ with Age
General Population Trends
Research consistently shows that IQ scores tend to decline with age. This decline manifests differently across various types of intelligence. Performance IQ, which involves problem-solving and processing speed, tends to decline earlier and more rapidly compared to verbal IQ, which involves language and knowledge-based skills. This pattern is observed in the general population, indicating a natural age-related cognitive decline.
Specific Age-Related Changes
Detailed studies using the Wechsler Abbreviated Scale of Intelligence-Second Edition (WASI-II) reveal that different subtests peak at different ages. Vocabulary and Similarities subtests, which measure verbal comprehension, show minimal variation with age, peaking between 30 to 54 years. In contrast, Block Design and Matrix Reasoning, which measure perceptual reasoning, peak earlier (17 to 44 years and 20 to 29 years, respectively) and then decline significantly. The Full Scale IQ remains relatively stable until around 65 years, after which a noticeable decline occurs.
Heritability and Environmental Influences
The Wilson Effect
The heritability of IQ increases with age, a phenomenon known as the Wilson Effect. Studies show that the heritability of IQ reaches an asymptote of about 0.80 by the age of 18-20 years and remains at that level into adulthood. Concurrently, the influence of shared environmental factors decreases significantly, stabilizing at around 0.10 by the same age. This suggests that genetic factors play a more substantial role in determining IQ as individuals age, while the impact of the environment diminishes.
Socioeconomic and Familial Factors
Socioeconomic status and familial factors also influence changes in IQ scores. For instance, children from disadvantaged urban areas show a significant decline in IQ from age 6 to 11, whereas children from suburban areas do not exhibit such a decline. This suggests that growing up in a disadvantaged community can negatively impact cognitive development more than individual or familial factors.
Longitudinal Stability and Variability
Stability Across the Lifespan
Longitudinal studies, such as the Scottish Mental Surveys, indicate that IQ scores can remain relatively stable from childhood into old age. However, the degree of stability can vary. For example, individuals with higher initial IQ scores tend to maintain their cognitive advantage throughout their lives. Similarly, the Munich Longitudinal Study on the Ontogenesis of Individual Competencies (LOGIC) found that IQ stability is higher for shorter intervals between measurements and increases with age.
Impact of Education
Education has a positive association with higher IQ scores later in life. Individuals with more education tend to have higher IQ scores in old age, although education does not appear to improve cognitive processing speed. This suggests that while education can enhance certain cognitive capacities, it may not affect more fundamental aspects of cognitive processing.
Special Populations
Intellectual Disabilities
In populations with intellectual disabilities (ID), the pattern of IQ change with age differs from that of the general population. Studies show that verbal abilities in individuals with ID decline more significantly than performance abilities, which is the opposite of the trend observed in the general population. This indicates that different mechanisms may be at play in cognitive aging for individuals with ID.
Flynn Effect Variability
The Flynn Effect, which describes generational increases in IQ scores, does not apply uniformly across all ages and ability levels. For instance, while younger adolescents (age 13) show an increase in IQ scores over time, older adolescents (age 18) exhibit a decline. Additionally, individuals with lower initial IQ scores show a decrease over time, whereas those with higher initial IQ scores show an increase. This variability challenges the notion of a uniform increase in IQ scores across generations.
Conclusion
In summary, IQ scores generally decline with age, with performance IQ declining earlier and more rapidly than verbal IQ. The heritability of IQ increases with age, while the influence of shared environmental factors decreases. Socioeconomic and familial factors, as well as education, play significant roles in cognitive development and aging. Special populations, such as those with intellectual disabilities, exhibit different patterns of IQ change. Understanding these dynamics is crucial for developing interventions to support cognitive health across the lifespan.
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