I’ve always heard that 100 is the “average” IQ, but I’m curious why that specific number was chosen. Is there something special about 100, or was it just an arbitrary decision when IQ tests were first created?
Also, how do they make sure that 100 stays the average over time if people’s scores are supposedly increasing (the Flynn Effect)? Do they have to keep adjusting the tests, or does the number just naturally stay at 100 somehow?
The number 100 was chosen purely for convenience, it’s easy to understand and work with. IQ tests are designed so that the average score in the population is always 100 by definition, with a standard deviation of 15 points. This means that no matter when or where you take a properly normed test, 100 represents average performance for that population at that time. To maintain this, tests get re-normed every 10-15 years using new representative samples. So when the Flynn Effect raises raw scores, the test publishers adjust the scoring so that the new average becomes 100 again. It’s a relative scale, not an absolute measure.
It’s basically just a convenient reference point. IQ tests are normed so that 100 is always the average and most people (68%) fall between 85-115. The number itself is arbitrary, they could’ve made it 500 or 1000, but 100 is simple. The Flynn Effect doesn’t change this because tests get re-standardized periodically. So if raw scores go up over time, they recalibrate the test so that 100 still equals average performance. That’s why your grandparents’ 100 isn’t the same as your 100 in terms of raw ability, the scale shifts to keep 100 as the midpoint.
@Marcelo I think the statement that “100 represents average performance… at that time” is the most crucial takeaway, as it directly counters the idea that 100 is some kind of universal, absolute standard. If the test is properly normed, doesn’t it follow that a person scoring 100 in one country should possess the same relative rank (the 50th percentile) as a person scoring 100 in another, even if the raw number of items they answer correctly is different?
When you put it simply, 100 isn’t a discovery about intelligence. It’s a decision about classification. And it reflects as much about society’s need to rank and label people as it does about how the mind actually works.
So in the end, 100 isn’t special because of human intelligence, no? The number also tells us more about our need for order than it does about the mind.
There is nothing special about 100 being average. It’s just chosen for convenience. I guess IQ test creators like me could set the average to some other number, but this convention was set in the 1910s, and there’s no good reason to change it.
Yes, IQ tests get “readusted” (or “renormed”) every so often to ensure that the average remains 100. This has been standard practice even since before the Flynn effect got its name.