average iq by age

Introduction

The relationship between age and IQ has been a subject of extensive research, with various studies examining how IQ changes over the lifespan. This synthesis aims to present key insights from multiple research papers on the topic of average IQ by age.

Key Insights

Heritability of IQ Increases with Age:
- The heritability of IQ increases with age, reaching an asymptote at about 0.80 at 18-20 years and continuing at that level into adulthood. Shared environmental influence decreases across age, approximating about 0.10 at 18-20 years and continuing at that level into adulthood.
IQ Stability in Autism Spectrum Disorder (ASD):
- In individuals with ASD, nonverbal IQ (NVIQ) scores tend to remain consistent from early childhood to young adulthood, although scores within the lower ranges of ability may decline from age 2 to 19.
Sex Differences in IQ Over Time:
- Girls have a slight IQ advantage over boys at ages 7 and 11, but by age 16, boys have a slight IQ advantage over girls.
IQ Changes in Adulthood:
- While Verbal IQ remains stable across ages 20 to 74 when educational attainment is controlled, Performance IQ and Full Scale IQ show declines with age.
IQ Constancy in Superior Intelligence:
- Children with superior intelligence (IQ of 140 or higher) show a tendency for IQ to decrease with age, with boys losing about 3 points and girls losing about 13 points over six years.
IQ in Juvenile Delinquents:
- Among juvenile delinquents, boys aged 14 and over tend to have a slightly higher mean IQ than those below 14 years, although this difference is not statistically significant.
IQ Stability in Williams Syndrome:
- In individuals with Williams syndrome, overall IQ remains stable with age, although Performance IQ tends to increase.
IQ Constancy in Normal Children:
- In normal children aged 5 to 13, Full-scale IQ remains relatively stable over yearly intervals, with no significant sex differences in the pattern of IQ changes.

Conclusion

The research indicates that while IQ can show some variability across different age groups and populations, certain patterns emerge. Heritability of IQ increases with age, and while verbal intelligence remains stable in adulthood, performance-related IQ may decline. Sex differences in IQ can shift over time, and specific populations, such as those with ASD or Williams syndrome, show unique patterns of IQ stability. Overall, IQ tends to remain relatively stable across different stages of life, with some variations depending on individual and contextual factors.

Summary

Introduction

Key Insights

Conclusion

Sources and full results

The Wilson Effect: The Increase in Heritability of IQ With Age

The heritability of IQ increases with age, reaching an asymptote of 0.80 at 18-20 years of age and continuing at that level well into adulthood, while shared environmental influence decreases across age.

Measurement of Nonverbal IQ in Autism Spectrum Disorder: Scores in Young Adulthood Compared to Early Childhood

Nonverbal IQ scores in individuals with autism spectrum disorder (ASD) generally remain within the average range from age 3 to 19, but actual scores decline from age 2 to 19.

A longitudinal study of sex differences in intelligence at ages 7, 11 and 16 years

At age 16, boys have an IQ advantage of 1.8 IQ points over girls, supporting Lynn's hypothesis that males develop higher average intelligence than females.

Age and WAIS-R intelligence in a national sample of adults in the 20- to 74-year age range: A cross-sectional analysis with educational level controlled

Intelligence declines in Performance IQ and Full Scale IQ from age 20 to 74, but not in Verbal IQ, even after controlling for education.

Do the Stanford-Binet Iq’S of Superior Boys and Girls Tend to Decrease or Increase with Age?

Children with IQ scores of 140 or higher tend to lose IQ points over time, while girls tend to gain IQ points over time.

Age and intelligence of a group of juvenile delinquents

Boys aged 14 and over have a slightly higher mean IQ than those below 14 years, but no significant differences were found between sexes.

The relationship between age and IQ in adults with Williams syndrome.

Adults with Williams syndrome show a stable overall IQ, but Performance IQ increases with age, suggesting that overall IQ may remain stable.

IQ Constancy and Age

IQ consistency and age show a perfect relationship, with correlations increasing with age, but no sex differences in IQ changes were observed.

Age and IQ effects on stimulus and response timing

Increased age and decreasing IQ tend to increase variability in judgments of duration, but overall accuracy in timing tasks remains generally consistent across groups.

IT, IQ and age: A comparison of developmental functions

Inspection time (IT) improves with childhood maturation, and is more related to mental age than IQ, in children with average and above average IQ levels.

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