IQ and age (part II)

In my last posting here, I provided a brief overview about IQ and age. The brain develops quickly in childhood and in early adolescence. It has been argued that the brain reaches its full cognitive ability potential by the age of 16. This is illustrated by the fact that high IQ societies such as Mensa measure all test takers who are 16 years and above on the same adult IQ scale.

I also wrote about how Binet’s old IQ quotient calculation method i.e. IQ = (MA/CA) x 100, where MA is the “Mental Age” of the test taker, while CA refers to the test taker’s “Calendar Age” is a useful tool for understanding the generation relationship between IQ and age. More specifically, children who are ‘fast’ or ‘bright’ for their age will have an MA > CA, which means that these children will be classed as having an IQ score of more than 100.  I also wrote about the break down of the Binet IQ quotient method as test takers enter into their late teens and 20s, and this problem is exacerbated for older test takers.

For this reason, all noteworthy IQ tests have gotten rid of the quotient calculation method, and instead replaced it with standard scores, where a mean and standard deviation is established for each test.

With the statistical upgrade to IQ testing, what have we learned about the interrelationship between IQ and age?

IQ and age: fluid intelligence data is clear

Firstly, fluid intelligence (Gf) – or our ability to solve novel problems, peaks in our mid 20s and begins to decline thereafter, This very finding actually calls into question the fairness of high IQ societies measuring the IQ of test takers of 16 and above on the same ‘adult’ scale. Based on this finding, and all else being equal, one would expect the average 25 year old to perform better than the average 16 year old.

The bad news however, is that fluid IQ declines thereafter and fairly rapidly in our late 40s. Again, the relationship between IQ and age is rainbow-shaped. That is, IQ will increase between the ages of 1-25, peaks and plateaus in our late 20s, and begins a gradual decline in our 30s, before falling more precipitously thereafter.

So coming back to these high IQ societies, it becomes clear again that the average 25 year old will be expected to have a higher fluid IQ than the average 50 year old.

In my next post, I will explain how this finding affects IQ testing methods and what it means for test takers.

In the meantime, you can test your fluid IQ here.