Well, I’m not sure an I.Q. can be below zero. After all, there is a lower limit on intelligence; a human cannot actually be dumber than a bag of hammers (true for pretty much any definition of intelligence, but especially true if defined as ‘that which is measured by an IQ test’). So all the people in non-responsive comas will have the same intelligence and therefore the same IQ. And since there’s been more than a couple of these kinds of people, it’s not correct to put them all 6 2/3 standard deviations away from the mean; they should all be put somewhere closer.
So there is a lower limit on IQ, and based on the calculations above, it’s going to be above zero.
Sure, you could redefine things so that completely unresponsive people aren’t considered part of the population to which IQ applies, but no matter where you set the bar, there are going to be a bunch of people that just clear the bar, with no way to say one is smarter or dumber than the other. So again, you’ll have a cluster at the bottom, and by the rules of assigning IQ, they can’t all be 7 deviations away.
Situations where the disadvantage of having a 75 IQ are significant are much more common than situation where the advantages of having a 125 IQ are significant.
Long before you reach that point you hit the place where people are unable to actually take the test. Given that 15,000-40,000 peoples are in a persistent vegatative state in the US, if we believe in a bell curve 15 standard deviation model, IQ’s below 34 don’t make much sense.
> Well, I’m not sure an I.Q. can be below zero. After all, there is a lower limit on
> intelligence; a human cannot actually be dumber than a bag of hammers (true
> for pretty much any definition of intelligence, but especially true if defined
> as ‘that which is measured by an IQ test’). So all the people in non-responsive
> comas will have the same intelligence and therefore the same IQ. And since
> there’s been more than a couple of these kinds of people, it’s not correct to put
> them all 6 2/3 standard deviations away from the mean; they should all be put
> somewhere closer.
> So there is a lower limit on IQ, and based on the calculations above, it’s going
> to be above zero.
No, Quercus, it is theoretically possible for a person to have an I.Q. that is below 0, although it would require there to be a vastly larger number of people being compared than have ever existed in all history. The following situation is theoretically possible, although I admit it’s pretty unlikely. Suppose in some future period humanity travels all over the galaxy. Suppose there are 10 billion inhabited planets and each of them has 10 billion people. Then there are 100 quintillion human beings in the galaxy. Suppose none of them are in non-responsive comas. Suppose it’s possible to completely rank all 100 quintillion of them so that it’s possible to say which of any two people are the smarter of the two. (Yes, I know how weird this is, but the fact is that it’s theoretically possible to imagine this situation.) Then there would be someone with a highest I.Q. of the 100 quintillion, and their I.Q. would be above 200 using the present scale where the average is 100 and the standard deviation is 15. Similarly there would be someone with the lowest I.Q., and their I.Q. would be below 0. Yes, this is a bizarre supposition, but it’s still theoretically possibly.
robert_columbia writes:
> And one of the big questions of our time is whether or not the Flynn Effect
> means that humanity is getting smarter on average.
We only know about the increase of I.Q.'s given by the Flynn Effect since about 1920, since before then there was no testing of groups of any significant size. So at most we can only say that the I.Q. has been increasing for the past 90 years. In fact, the increase has been more patchy than that. The general supposition is that the Flynn Effect has something to do with a change in culture rather than any biological change.
Interesting discussion, I have never explored the intricacies of IQ scores before. When I was about 14 I did a test in exam conditions at the University of London and scored 176. Then I promptly got very average test scores in my various school exams. Although I like to think I’m more intelligent than average, from my life experience, I can only deduce that a high IQ means only that one is good at IQ tests. Not a very useful thing to excel at.
To a first approximation, everyone has the same sized brain and it works at about the same speed. Yes, some people are sharper than others, but the differences may be more subtle than they first appear–they might have traded one talent for another (e.g., the stereotypical antisocial nerd). So while one person may be 10x as capable as another for a given talent, no one is 10x as smart as another overall. The average brain just isn’t that bad, and no one is born with a 10 kg brain.
On the other hand, it’s easy for a brain to be defective. It doesn’t take much at all to have an unmeasurably low IQ, or to have a problem that degrades cognition by 50%. In other words, the low end has infinite dynamic range, while the dynamic range on the high end is probably 2x at best.