Is iq stable
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The Stability of IQ: Insights from Recent Research
Stability of IQ in Low Intellectual Ability
Research indicates that IQ stability in individuals with low intellectual ability (IQ < 80) is relatively high. A meta-analysis of commonly used IQ tests, such as those derived by Wechsler and Binet, found weighted-mean stability coefficients of .77 and .78 for Verbal IQ (V IQ) and Performance IQ (P IQ), respectively, and .82 for Full-Scale IQ (FS IQ) over an average test-retest interval of 2.8 years. However, it is noteworthy that while most Full-Scale IQs changed by less than 6 points, 14% of individuals experienced changes of 10 points or more, suggesting that IQ assessments should be approached with caution.
Genetic and Environmental Influences on IQ Stability
IQ remains relatively stable throughout life, with genetic factors playing a significant role. Studies using bivariate genetic models on kinship pairs from longitudinal samples have shown that 66% to 83% of IQ stability can be attributed to genetic factors. Additionally, 43% to 69% of changes in IQ are also due to genetic influences. The remaining stability and changes are influenced by shared and nonshared environmental factors. Interestingly, there are notable race differences in the genetic and environmental contributions to IQ stability.
Influence of Early IQ on Long-Term Stability
IQ stability from early childhood into adulthood varies depending on initial IQ scores. Research involving preterm and term-born individuals indicates that those with low IQ scores at preschool age exhibit more stable IQs from childhood into young adulthood compared to those with medium or high initial scores. This pattern suggests that individuals with initially high IQs may not maintain their relative advantage as others catch up over time.
IQ Stability in Low-Birthweight Individuals
Studies on low-birthweight individuals show that IQ remains stable from childhood to adulthood. For example, stability quotients for Verbal, Performance, and Full-Scale IQs were found to be 0.86, 0.86, and 0.89, respectively, in one sample, and 0.66, 0.65, and 0.74 in another. These findings suggest that most low-birthweight children maintain stable intellectual development patterns from middle childhood to young adulthood.
Differential Stability Based on Initial IQ Levels
Longitudinal studies have shown that IQ stability is generally higher for individuals with lower initial IQ scores compared to those with higher scores. For instance, children with initially high IQ scores tend to maintain their advantage into early adulthood, but the stability of their IQ scores is lower compared to those with initially low IQ scores. This trend highlights the importance of considering initial IQ levels when assessing long-term intellectual development.
Verbal vs. Nonverbal IQ Stability
Research indicates that Verbal IQ scores tend to be more stable than Nonverbal IQ scores, especially in children under ten years of age. This finding underscores the need for caution when interpreting nonverbal IQ scores over long periods, as they may be less reliable indicators of cognitive stability.
IQ Stability in Special Populations
In populations with specific conditions, such as developmental dyslexia, IQ stability can vary. For example, dyslexic individuals may experience a significant decrease in Verbal IQ over time, potentially due to less experience with reading and writing. Conversely, their Performance IQ may improve, possibly as a compensatory mechanism. These findings suggest that special education and tailored interventions are crucial for supporting the intellectual development of dyslexic individuals.
Conclusion
Overall, IQ tends to be relatively stable across different populations and developmental periods, with genetic factors playing a significant role in this stability. However, initial IQ levels, environmental influences, and specific conditions can affect the degree of stability. These insights highlight the complexity of IQ development and the need for careful interpretation of IQ assessments over time.
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