Do IQ Scores Change With Age?

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Written by Consensus
March 17, 2020 7 min read

Do IQ scores change with age?

 

Answer

Check out this answer from Consensus:

In conclusion, the research suggests that IQ scores can be stable across the lifespan, but this stability can be influenced by various factors such as the type of test used, the presence of developmental disorders, and genetic factors.

The relationship between age and IQ is complex and warrants further investigation to fully understand the underlying mechanisms.

Do IQ Scores Change with Age?

Intelligence Quotient (IQ) is a measure that has been widely used to assess human intelligence. The question of whether IQ scores change with age has been a subject of interest in psychological research for many years. This article will explore the findings from various studies that have investigated the stability and variability of IQ scores across different age groups.

Stability of IQ Scores in Young Autistic Children

Research on autistic children has shown that IQ scores during preschool years are quite stable and predictive of later IQ scores. This stability is particularly evident when the same test is used at both assessments and when children are 4 years or older at the initial assessment 1. However, the predictability of IQ scores can be affected by the type of test used, especially when comparing early scores on the Bayley Scales of Mental Development with later scores on performance or nonverbal tests 1.

The Wilson Effect

The heritability of IQ, which refers to the proportion of intelligence that can be attributed to genetic factors, has been found to increase with age. This phenomenon, known as ‘The Wilson Effect,’ suggests that by the age of 18-20 years, the heritability of IQ reaches an asymptote of about 0.80 and remains at that level into adulthood. Concurrently, the influence of shared environmental factors on IQ decreases, approximating about 0.10 at 18-20 years of age 2.

Long-Term Stability of IQ

The Scottish Mental Surveys of 1932 and 1947 provide a unique perspective on the stability of IQ scores from childhood to old age. The data from these surveys have shown that IQ scores are remarkably stable across the lifespan. This research has also explored the impact of childhood intelligence on survival, health, and cognitive change in old age 3.

Nonverbal IQ in Autism Spectrum Disorder

In individuals with autism spectrum disorder (ASD), nonverbal IQ (NVIQ) scores in young adulthood compared to early childhood have shown that most adults who scored in the range of intellectual disability also received scores below 70 as children. While the majority of adults with average range scores had scored in this range by age 3, actual scores within the lower ranges of ability declined from age 2 to 19 4.

Age Differences within Secular IQ Trends

The secular trend in IQ, which refers to the observed rise in IQ scores over time, has been examined in relation to age. While the overall secular pattern in IQ has not changed, the role of age within this pattern has evolved. The decline in test scores that occurs when new norms replace older ones was smaller for older children in earlier testings, but these age differences have disappeared in more current testings 5.

IQ Effects on Stimulus and Response Timing

A study on older participants with known scores on the Culture Fair Intelligence Test found that increasing age and decreasing IQ were associated with increasing variability of judgments of duration. However, the ability to time events accurately on average was not significantly affected by age or IQ 6.

Predicting Scores in Older Adults

Regression equations have been developed to predict scores on various neuropsychological tests based on age, gender, and estimated premorbid IQ. These equations, which account for 10% to 30% of the variance in test scores, can be used to interpret data from older persons and assess the abnormality of the difference between predicted and obtained scores 7.

IQ Change in Institutionalized Mentally Retarded

A study investigating IQ change in an institutionalized mentally retarded population found that contrary to previous research, Full Scale IQ did not decrease with age. There were slight increments in scores, more consistent in Performance than Verbal IQ 8.

Age and IQ in Adults with Williams Syndrome

In adults with Williams syndrome, age-corrected scaled scores remained stable with age, indicating a developmental trajectory similar to that of the normative sample. However, increased age was related to higher Performance IQ, suggesting that the overall IQ of an adult with Williams syndrome will likely remain stable 9.

 

Do IQ scores change with age?

Louis Matzel has answered: Unlikely

An expert from Rutgers University in Genetics, Psychology, Neuropsychology

Although IQ can change for an individual, across a population it is well established that IQ is stable across the lifespan. This does NOT mean that our abilities do not change as we age. IQ (as the name indicates) is a QUOTIENT, i.e., your score is calculated relative to persons of your age. If your IQ is high relative to other 20 year-olds, it is very likely to be high relative to your age-matched peers when you are 90 years old. Likewise if your IQ is low. Nevertheless, we are all much less capable at 90 than we were at 20 (cognitive aging is real and it is profound) . But since IQ scores are age-normalized, your IQ score will remain relatively constant. Abilities change, but IQ scores tend to be very stable.

 

Do IQ scores change with age?

Hynek Cígler has answered Extremely Unlikely

An expert from Masaryk University in Psychology, Quantitative Psychology, Psychometrics, Intelligence

However the intelligence ability is changing during the life, the IQ (intelligence quotient) does not. This measure is defined to have mean of 100 in each age group. So the average IQ e.g. in the age 5 is 100, and the same in the age 50.

The intelligence (ability itself) increases till the age 20-50 (based on the intelligence factor), while after that point it decreases. The highest point differs across people and it also depends on the intelligence factor (“type of intelligence”).

 

Do IQ scores change with age?

Julia Strait has answered: Near Certain

An expert from Stepping Stone Therapy in Psychology, Traumatology, Anxiety

Yes, the scores can change in several ways:

  1. Research has shown that IQ scores are not stable, as previously thought, and one study even showed that teens’ IQ scores can change up to 21 points (more than one standard deviation, or the amount required to jump from “Average,” say, to Intellectually Disabled, or Gifted). (Read a story about this study here: https://www.theguardian.com/science/2011/oct/19/teenagers-iq-scores-adolescence)
  2. A large body of research shows that different IQ subscales show different patterns of change with age. Verbal or crystallized intelligence increases relatively steadily with age. However, nonverbal or fluid intelligence improves until the mid-20s to 30s and then slowly declines with further aging.
  3. Only about 50% of IQ is heritable. Thus, environmental influences (shared and especially nonshared) contribute to improvements or declines in IQ across development. These influences change over time and impact IQ scores.
  4. Certain traumatic brain injuries, including brain damage due to environmental toxins like lead, can lead to quite dramatic drops in IQ in short periods of time.
  5. There is growing evidence that adverse childhood experiences, most notably child maltreatment (abuse and neglect), can negatively impact overall IQ scores as well as scores on IQ test subscales, such as verbal memory and processing speed.
  6. IQ scores do not reflect a “true score” but an estimate. All estimates include error, so IQ scores include error, too. Your score may change though your underlying “true” intelligence does not. That’s why most IQ tests provide a range (called a Confidence Interval) in which your “true” IQ likely falls. The score will change slightly each time you are tested. Each IQ test and score, subscale score, etc. fluctuates within a certain range depending on the reliability of the particular test–usually plus or minus the standard deviation of that test.

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