Tuesday, 10 July 2012

Problems with measuring very high IQ





1. Ceiling effect.






2. Problems with norming.













4. Problems with discriminating between ultra-high IQ people. 
In sum -
IQs differences above about 130 are only approximate.
Extremely high cognitive ability is usually specific rather than general; 


dearieme said...

Thank you for that excellent summary. I was told once that when J J Thompson was appointed Master of Trinity, some arts don harrumphed "but he's not even intelligent". I dare say that the story is told of other people too.

J said...

It is also very difficult to measure very low IQs too. Pygmies, for exaple, are measured very low, yet they hunt and survive in a very complex jungle environment. They build complex bridges and hunt elephants. There are morons but no stupids.

bgc said...

@J -This is not so difficult - in the sense that it is possible to go back to the old method of using a comparison of chronological age with test performance - so that an average pygmy might perform in a range of cognitive tests at the same level as the average 8 year old English child - therefore they would have an IQ of 50 (on the old assumption that IQ performance reaches a ceiling at age 16 - but in fact it is later than 16 for men).

Jonathan C said...

Perhaps another way to express your first point (ceiling effect) is to point out that you can't distinguish between a 180 IQ and a 210 IQ by simply asking more questions of the sort that distinguish between a 100 IQ and a 130 IQ; you need different questions that can discriminate at that level.

But what would those questions be? I can imagine you could ask them to prove mathematical theorems with difficult proofs. But as per your third point (specialized abilities), that test would only work if the test-takers have enough familiarity with the mechanics of proving math theorems.

It seems to me that you are implying that there might be no "general" questions that would distinguish between a 180 and a 210 IQ.

bgc said...



"To add to what our host said, I was watching a documentary about Liberia, and I was thinking, "This is what a society where most people are eleven would look like if you gave them a lot of guns, drugs, and access to free clothes and food…"

"In other words: Their incentives are all to steal and wreak havoc, and there isn't the level of potential organization for one gang to just dominate the others without outside help...

"I couldn't find a number for Liberia, but if we take its neighbors Sierra Leone and Guinea as stand–ins… you're looking at a median IQ in the mid–60s. So a society of eleven year olds wasn't too far off–base.

I think this puts an interesting light on the "child–soldier" phenomenon as well... "

bgc said...

@Jonathan C - Here is an example of how people have approached the problem of finding tests to discriminate among ultra-high IQ people


This is a fascinating problem, and the people that can do this kind of test are very interesting - but there is a strong sense that we are talking about some specialist ability qualitatively different from that which differs between individuals near to the average.

Simon said...

bgc, what is your take on variation in IQ; what is its purpose?

bgc said...

@Simon - It is presumably a mixture of adaptation with the effects of pathology/ disease (which could pull-down IQ).

Dona Matthews said...

delightful article, well-said!-- thank you!

Zontar said...

It's worth pointing out that your point 3 is called "Spearman's Law of Diminishing Returns"