Does IQ change as you get older?

IQ and ageAs different people and you will get a different answer. Some say that IQ and age are not related variables. But you look at the data more closely and you can see that the answer is clearly “yes they can change – to some degree”.

Children go through periods of very rapid mental development, so unsurprisingly, mental development and IQ can change year on year for young children.

For Groups, IQs have been shown to be fairly constant from early adulthood through to adulthood (Salter 2008).

  • The coefficient of correlation between IQ at age 5 and IQ at age 40 is 0.50-0.60 (i.e.55%)
  • The coefficient of correlation between IQ at age 9 and IQ at age 40 is 0.70 (i.e. 70%)
  • IQs at ages 10 &12 predict IQs at ages 17 & 18 at a correlation coefficient of 0.98 (i.e. 98%)

Although it is not yet fully established scientifically whether puberty is a defining moment from a brain development standpoint, intuition and statistics suggest that it might be. From Salter’s study, it is clear that IQs at ages 10-12 (very close to puberty) are much better predictors of IQs in adulthood.

There is clearly a relationship between IQ and age.

So it’s not just about ‘feeling good’ on test day which may impact the result of your IQ test, but rather the admission that people’s IQs tend to change slightly over time.

Several studies on ageing have also been performed which suggests that fluid intelligence (i.e. the ability to solve novel problems) may peak in the mid-to-late 20s, whilst crystallized intelligence (i.e. the ability to retain and apply formal educational instruction) may peak in the mid-50s.

So people who argue that IQs are fixed and immutable are simply wrong. There should be no doubt about the fact that IQ and age are related variables. On an absolute basis, IQs vary quite substantially during our lifetime and lifestyle choices can impact the growth of IQ (e.g. learning new skills or remaining longer in formal education can increase IQ) or precipitate its decline (e.g. unhealthy lifestyles or taking drugs). But ipsative IQ tests should be comparing your test scores against those of people in your age bracket to give you a true representation of how bright you are relative to the relevant population subset. When using ipsative tests only, your IQ is likely to be much more stable than would otherwise be the case. In summary, IQ and age are related and is it wrong to think that your IQ will never change as you get older.

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