At what age does iq become stable
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Age of IQ Stability: Insights from Longitudinal Studies
Early Childhood IQ Stability
Research indicates that IQ begins to show signs of stability from preschool age. Studies have demonstrated that IQ scores obtained at around 4 years old can moderately predict IQ scores in later childhood and adulthood. For instance, a study involving preterm and term-born individuals found that IQ at 4 years correlated significantly with IQ at 9, 14, and 44 years, with stability coefficients ranging from 0.48 to 0.73. This suggests that while there is some fluctuation, early IQ assessments can provide a reasonable indication of future intellectual performance.
Middle Childhood to Adolescence
The stability of IQ increases as children grow older. By middle childhood (around age 9), IQ scores become more stable and predictive of future IQ. For example, a study on low-birthweight subjects showed high stability quotients (0.86) for IQ scores measured at age 9.5 and retested at age 23.5. Similarly, another study found that IQ stability was higher for shorter intervals between measurement points and increased with age, indicating that the rank ordering of individuals' IQs becomes more consistent as they approach adolescence.
Adolescence to Early Adulthood
IQ stability continues to strengthen into adolescence and early adulthood. Research from the Munich Longitudinal Study on the Ontogenesis of Individual Competencies (LOGIC) found that IQ stability was moderately high from ages 4 to 23, with higher stability for shorter intervals and increasing stability with age. Additionally, the Scottish Mental Surveys revealed that about half of the individual differences in intelligence remain stable from childhood to old age, suggesting a significant degree of stability from adolescence onwards.
Factors Influencing IQ Stability
Several factors influence the stability of IQ over time. Initial IQ scores play a crucial role; individuals with low initial scores tend to show more stable IQs from childhood into young adulthood compared to those with medium or high initial scores. Moreover, the type of cognitive abilities measured can affect stability. For instance, in individuals with autism spectrum disorder (ASD), verbal IQ and working memory stabilize by early adulthood, while nonverbal and perceptual scores continue to change.
Conclusion
In summary, IQ begins to show stability from preschool age, with increasing stability through middle childhood, adolescence, and into early adulthood. By around age 9, IQ scores become significantly stable and predictive of future intellectual performance. Factors such as initial IQ scores and the type of cognitive abilities measured can influence the degree of stability. Understanding these patterns can help in educational and vocational planning, providing insights into the long-term development of intellectual abilities.
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