How many people in the world have low IQ?

Answer 1

All the controversy over the meaning and usefulness of IQ aside, the average IQ is 100 by definition. The distribution of IQ appears to follow a normal (bell) curve and therefore the well understood characteristics of normal curves allow us to make some good estimates. Considering this definition, average performance on an IQ measure (a measure or an instrument- not a test- that has good validity and reliability) is always 100. There will always be, even if the general 'intelligence' of the population is changing, 50% of the population above average and 50% below average. From here you decide what you mean by "low IQ".

It seems unreasonable to assume that any IQ below 100 should be defined as 'low', since we are talking about part of the normal curve of intelligence where the great majority of people fall. Also, no person would consider an IQ of 105 to be 'high', so it is callous and ignorant to consider an IQ of 95 to be 'low'. You might define (it is mostly arbitrary) the average range of IQ as falling within one standard deviation of the mean (85 to 115), or perhaps one and a half standard deviations (roughly 78 to 122).

Usually the standard deviation of IQ is defined as 15. Then by studying the characteristics of normal curves you can arrive at a reasonably good estimate of the percent of individuals who would fall below your arbitrary cut-off. Considering the range of one standard deviation above and below average, IQ's of 85 to 115, we can estimate that close to 68.2 or 68.3 percent of the population falls within this range. Also, we can estimate that about 15.9% of the population falls below this range, and about 15.9% of the population falls above it. Perhaps these estimates suit your need.

Whatever your need happens to be, don't fall into the trap of glorifying IQ, a tendency that probably increases as IQ's themselves increase. They are very useful over a limited range of applications, and beyond that hard work needs to kick in. No one should feel entitled because of an artificial estimate of 'intelligence'. As the saying goes, "IQ is what IQ instruments measure", whatever that means. IQ's do not and should not define anyone.

Brief note on the average and standard deviation: The numbers 100 and 15 are completely arbitrary but generally accepted. You could choose, if you want, 917 as average with a standard deviation of 71, or any other numbers. These numbers are then treated mathematically so that they allow the same valid analysis of the population used in developing the instrument. Virtually the same individuals represented in the 85 to 115 IQ above would be the ones represented by the measures 846 to 988 in our whimsical scenario.

Answer 2

It is difficult to accurately estimate the number of people in the world with low IQ, as IQ assessments can vary and are influenced by factors like culture and socioeconomic status. However, some studies suggest that around 15% of the global population may fall into the category of low IQ.