Does IQ Decrease With Age?

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Does IQ decrease with age?

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The relationship between age and IQ is multifaceted, with various factors influencing cognitive abilities over the lifespan. While some aspects of intelligence may decline with age, others remain stable or even improve. The Wilson Effect highlights the increasing role of genetic factors in determining IQ as individuals age, while studies on brain aging and cognitive performance suggest that neuroanatomical decline does not necessarily lead to cognitive deterioration. Overall, the evidence indicates that IQ does not uniformly decrease with age, but rather exhibits a complex interplay of stability and change.

The relationship between age and intelligence quotient (IQ) has been a subject of extensive research. While some studies suggest a decline in certain cognitive abilities with age, others indicate stability or even improvement in specific aspects of intelligence. This article aims to explore the complex dynamics between aging and IQ, drawing on findings from multiple research studies.

The Wilson Effect

One of the key concepts in understanding the relationship between age and IQ is the Wilson Effect, which posits that the heritability of IQ increases with age. According to a study by Ronald Wilson, the heritability of IQ reaches an asymptote at about 0.80 at 18-20 years of age and continues at that level well into adulthood. This suggests that genetic factors play a more significant role in determining IQ as individuals age, while the influence of shared environmental factors decreases.

Age-Related Changes in Brain Structure and IQ

A longitudinal study examined the relationship between brain aging and psychometric intelligence in a sample of 231 older adults over four years. The study found significant declines in grey matter (GM) and normal appearing white matter (NAWM) volumes, with annual percent changes of -0.73% and -0.79%, respectively. However, verbal and non-verbal IQ measures remained stable, indicating that neuroanatomical decline does not necessarily correlate with cognitive deterioration.

Performance Variability in Older Adults

Research on the effects of aging and IQ on stimulus and response timing found that increasing age and decreasing IQ were associated with greater variability in judgments of duration. Despite this, older adults could time events accurately on average, suggesting that while there may be increased variability, the overall ability to perform certain cognitive tasks remains intact.

The Flynn Effect and Age

The Flynn Effect, which describes generational increases in IQ scores, may not be consistent across all age groups. A study involving 10,000 U.S. adolescents found that while IQs increased by 2.3 points at age 13, they decreased by 1.6 points at age 18. This indicates that the Flynn Effect may reverse in late adolescence, challenging the notion of a uniform increase in IQ across all ages.

IQ Stability in Specific Populations

In individuals with Williams syndrome, a study found that while raw scores on IQ subtests showed both increases and decreases with age, the overall age-corrected scaled scores remained stable. This suggests that the developmental trajectory of IQ in this population is similar to that of the general population, with overall IQ remaining stable into adulthood.

Memory and Cognitive Processing

A study examining the effects of aging and IQ on memory tasks found that IQ had a significant impact on performance, particularly in recognition and recall tasks. However, age had a more substantial effect on boundary separation and non-decision time, indicating that while cognitive processing speed may decline with age, the accuracy of memory tasks is more closely related to IQ.


Does IQ decrease with age?

Alan S. Kaufman has answered Likely

An expert from Yale University in Intelligence, Education

The question of how our IQs change has been researched in numerous research investigations, often using the various versions of the Wechsler Adult Intelligence Scale (WAIS), the most recent being the 2008 WAIS-IV. The results have been confirmed many times, but the research is a little tricky to conduct for two reasons: 

(A) IQs are always calculated relative to a person’s age, whether that age is 10, 15, 25, 50, 72, or 88. So 25 year olds are compared to other 25 year olds in terms of the number of items they answer correctly on any given task just as 50 year olds are compared to other 50 year olds. For every age group, the average or mean IQ is set at 100. So we can’t directly compare the mean IQs across the adult age range because—by definition—every group will average 100. 

(B) the second hitch is that different age groups differ in their education level. It is more common now than 25 or 50 years ago for people to attend college and to earn degrees. Since education is related to IQ, that variable serves as a confound in the research. If IQs go down with age, how can we be sure that any decrease is due to age rather than the lower level of education, on average, for older than younger adults? 

Both of these problems are easily handled by researchers (I have conducted a number of these investigations with my colleagues). The first thing we have to do is to find a common “yardstick” to compare adults. We can compare the performance of 70 year olds, 60 year olds, 50 year olds, 40 year olds, etc. to the norms (reference group or standards) established for young adults. 

In my research, we define young adults as about age 30 (usually ages 25-34). In that way, young adults will have an average IQ of 100 because that is the way the norms are developed. When we compare adults across the life span to young adults that will tell us how IQ changes as we get older. But first we have to take care of the inequity in education across the age range. That can be done statistically by “controlling” for education (even though many more 30 year olds graduated college and many more 70 year olds dropped out of high school, this statistical procedure controls for the age to age differences. 

Now we can compare Full Scale (global) IQs for adults of different ages. A clear decline is evident. The mean WAIS-IV IQ is 100 for ages 20-24 and is 99 for ages 25-44. Then it drops to 97 for ages 45-54, to 94 for ages 55-64, to 90 for 65-69, to 86 for ages 70-74 and to 79 for ages 75+. 

But global IQ is an amalgam of different kinds of intelligence, the most popularly studied being fluid intelligence and crystallized intelligence which together—along with abilities called working memory and processing speed—are combined to yield global or Full Scale IQ. Fluid intelligence or fluid reasoning (abbreviated Gf) reflects the ability to solve novel problems, the kind that aren’t taught in school, whereas Crystallized intelligence or crystallized knowledge (Gc) measures learning and problem solving that are related to schooling and acculturation. And they have very different aging curves. 

Gc averages 98 at ages 20-24, rises to 101 by ages 35-44, before declining to 100 (ages 45-54), then 98 (55-64), then 96 (65-69), then 93 (70-74), and 88 (75+). 

The decline with age in Gf—solving novel problems—is even more precipitous. Gf peaks at ages 20-24 (100), drops gradually to 99 (25-34) and 96 (35-44) before starting a roller coaster plunge to 91 (45-54), 86 (55-64), 83 (65-69), 79 (70-74), and 72 (75+). 

These values are just averages for the entire US population of adults, with the mean IQs for each age higher for more educated individuals. But the same rate of decline across the age range seems to occur for all adults, on average, whether they are semi-skilled workers or university professors. 

Two sources to consult for those interested: Essentials of WAIS-IV Assessment—2nd edition (Elizabeth Lichtenberger & Alan Kaufman), 2013, John Wiley publisher and IQ Testing 101 by Alan Kaufman, 2009, Springer publisher.


Does IQ decrease with age?

Ian Silver has answered Unlikely

An expert from University of Cincinnati in Intelligence, Behavioural Science, Social Sciences

Intelligence, like most psychological characteristics, is highly heritable. Habitability refers to the percentage of the characteristic that is accounted for by genetic factors. Approximately 67 percent of intelligence is influenced by genetic factors. In addition to these genetic factors, research has show that early life factors, such as household characteristics, influence intelligence. Approximately 10-12 percent of intelligence is influenced by these early life factors. An important characteristic of genetics and early life factors is that they don’t tend to change as we age. As such, if approximately 77-79 percent of intelligence is influenced by factors that don’t change as we age, it is unlikely for our level of intelligence to decrease as we age. Negative environmental stimuli (e.g., head trauma) and serious diseases, however, can result in declines in general intelligence. The influence of these factors can correlate with age but aging alone does not influence intelligence.


Does IQ decrease with age?

Nachshon Meiran has answered Uncertain

An expert from Ben-Gurion University of the Negev in Intelligence

I had to choose among the options which is why I chose “unlikely”. However, the real answer is more complex in my mind.

IQ indicates the relative positioning of an individual relative the the average. This relative positioning is extremely stable. A quite recent paper in Psychological Science (to the best of my memory) found a correlation of almost .70 between IQ at age ~11 to that at age ~90.

HOWEVER, the population averages are influenced by age. The best supported factorial model of intelligence is Carrol-Cattel-Horn model, according to which there are several specific abilities such as fluid, crystalized, auditory, visual, quantitiative, and speed. All of these abilities are explained by the general factor, g’. Now, all the specific abilities but one (crystalized intelligence) decline from age ~25-30 (i.e., the population average) – some (speed) decline quite dramatically.


Does IQ decrease with age?

Michael Thomas has answered Unlikely

An expert from Birkbeck, University of London in Psychology, Cognitive Science, Intelligence

Intelligence is usually measured by a set of tests, for instance, some about language skills, some about non-verbal skills such as solving puzzles, some about how quickly you can complete a task. Your intelligence will be the average of your scores across the tasks, compared to how well other people do. The concept of ‘general’ intelligence arises because a person’s scores across the set of tests tends to be similar. As you age, different skills change at different rates.

The fastest response times you will ever have are in your mid-twenties, but (so long as you don’t develop dementia), your knowledge of vocabulary will increase throughout your life. Into your late sixties, most cognitive skills relying on things you have learned (so-called crystalised knowledge) either increase or are pretty resilient. The speed with which you can do things can decline.

The short answer, then, is that your skills may diverge with age, but your overall intelligence can remain similar. For more information on whether IQ is fixed, take a look at the Centre for Educational Neuroscience’s resource:


Does IQ decrease with age?

Gavin Brown has answered Uncertain

An expert from University of Auckland in Education, Psychometrics, Statistics

Previous answers have correctly shown that certain aspects of cognitive functioning decline with age. furthermore, they were correct that with continued development of crystallised knowledge the slowing of those functions is not really apparent. However, with age comes greater probability of diseases that can impact IQ. So the answer really is uncertain; it depends on your health and how and if you continue to use your mind. If you want to know how to keep your mind going, Lord Robert Winston gives excellent advice in his book. Doing puzzles — sudoku, bingo, jigsaws, etc.–will keep your mind active solving new problems; this fights mental atrophy. Diet and exercise do too.

Winston, R. (2003). The Human Mind and How to Make the Most of It. London: Bantam.

Plus, something we often forget is that people with below average IQ tend not to survive into old age as frequently as those with above average IQ. So developing your IQ as young as possible will help you age longer and better. In good health, overall IQ does not necessarily diminish–but speed of processing will.

It depends…..

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