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Decline or Increase in IQ Scores

By Inderbir Kaur Sandhu, Ph.D

I have had numerous letters and friends asking about the possibility of a drop in IQ scores that I have decided to write a short article on this issue. I hope this will answer some of the questions you have in mind.

Researches have indicated that there is a possibility of IQ scores varying throughout a person's lifetime, in fact as much as 20 points! There are many reasons that can account for a change in an individual's IQ scores, from growth spurts to emotional or personal problems. A high IQ may be a peak of intellectual potential. It is advisable that parents do not panic if testing shows a drop in IQ, especially if the drop is not too drastic. Achievement scores maybe a different matter, and parents should investigate decline in these scores.

Can IQ scores change?

Yes, it can, though not drastically in a short period. Especially during infancy and early childhood, there is a possibility of change in IQ scores frequently. However, IQ scores begin to stabilize in middle childhood. Furthermore, by the age of approximately 7 years, childhood IQ scores are found to be rather good predictors of adult IQ.

How does age affect our IQ?

In reality, standardized IQ test scores are converted from raw scores to scaled scores using a conversion table (See the IQ scores classification here). This takes into account the mental ability over age of the test taker which ensures that the mean IQ for the population remains 100 across the life span (based on the bell-curve). As we age (as early as 30!), some of our mental performance may be affected and this would be reflected in our scores (depending on the tasks that make up IQ tests). With this, good IQ test scores takes into account changes in mental ability over age by modifying the IQ score, which in turn, shows little decline in IQ scores (assuming other factors remain the same).

What affects human IQ?

Good parenting influences intellectual development
Parents should provide developmentally appropriate play and learning materials, encourage exploration & stimulate curiosity, create a warm, responsive and supportive environment. For optimal intellectual development, appropriate stimulation, structure, support and early intervention is essential.

Poverty raises the risk of poor intellectual development
Poor nutrition, low maternal education, unemployment, inadequate living conditions, limited educational opportunities, poor health

Environmental factors
Plays a role in determining IQ. Individuals born prematurely, of low birth weight or with other obstetric hazards have lower IQ than the general population. Growing up in a racially segregated and disadvantaged community, more than individual and familial factors, may contribute to a decline in IQ score in the early school years.

School attendance
Don't be surprised! Research has indicated that intelligence influences our decision to stay in school; in fact staying in school possibly prevents a drop in IQ. Having said that, naturally delayed schooling also affects IQ. In fact, studies have even shown that IQ is affected by vacations which show a systematic decline in IQ scores over the holiday months. This proves that each day away from school especially for children whose vacations are least academically orientated, decline is seen, however, rather marginal and possibly temporary.

Size of head
Sounds impossible but research have proven this. IQ is positively correlated with the size of one's head (in terms of cranial volume).

IQ tests!
But, of course! Different tests may indicate different scores. However, it is expected that standardized and reliable tests should not show much difference. Different tests also may test different sets of abilities.

A note on The "Flynn Effect"

In his study of IQ tests scores for different populations over the past sixty years, James R. Flynn discovered that IQ scores increased from one generation to the next for all of the countries for which data existed (Flynn, 1994). This interesting phenomenon has been called "the Flynn Effect". Flynn believes that the increase is actually an increase in abstract problem solving rather than intelligence. Otherwise, someone who scored among the best 10% a hundred years ago, would today be among the 5% weakest. In short, someone (maybe our great grandfathers!) who would be considered very bright a century ago, should now be considered a moron!

As Flynn and other researchers found, this is probably due to environmental factors when taking a test such as:

Education increase in levels of education, longer formal schooling years, and increase in culture-free IQ tests

Societal changes - possibility that people have learned to work better within a limited time frame, which allows later generations to score better on timed tests because they make intelligent guesses. In addition, probably over the years they also become more exposed to the kind test items in an IQ test.

Better health and nutrition over the years, there has been a marked improvement in worldwide nutrition. This simply implies that better nourished brains would allow subjects to perform better on IQ tests as well as in everyday activities.

Parenting - parents these days tend to pay much more attention to their children, thus stimulating their cognitive development. This is possible because parents tend to have fewer children to care for, to have more free time, to be wealthier, to be better educated, and to have a better insight in the needs of their children.

Complexity of life today's society as a whole functions at a higher intellectual level, proposing to the curious child more information, more intellectual challenges, more complex problems, more examples to be followed, and more reasoning methods to be applied. In addition, more reading materials, media stimulation, enhanced everyday appliances. All these demand a more abstract type of reasoning.


Flynn, J. R. (1994). IQ gains over time. In R. J. Sternberg (Ed.), Encyclopedia of human intelligence (pp. 617-623). New York: Macmillan.
Flynn, J. R. (1999). Searching for justice: The discovery of IQ gains over time. American Psychologist, 54, 5-20.


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