Intelligence, as measured by IQ tests is distributed throughout the human population like height and many other physical characteristics. Most men have a height that deviates a small amount from the average adult male height. In the US, the average male height is 5′9.5″. This means that 50% of American males are at or below 5′9.5″ in height and 50% are above that height. However, of the 50% above 5′9.5″, only about 14.5% of American males are over 6 feet tall. This means that most males have a height close to the average, but as we move farther away from the average height, the number of people in that group becomes much smaller. That is, there are few people who deviate significantly from the average. We say that human height is “normally distributed.” Similarly, intelligence, as measured by IQ tests is normally distributed; most people have IQ that is close to the average of 100. The gifted and the intellectually challenged represent a small portion of the total population, i.e., they are relatively rare. The graph below (from Intelligence, IQ & perception – Intelligence and IQ ) expresses this “rarity” quantitatively.
The graph shows that only about 2.4% of the human population has IQ above 130 and are designated as “gifted.” In high schools in the US, high-performing students (those with good grades) are listed on the honor roll. While the percentage of students on the honor roll varies across schools, it is often around 20%. This means that a lot of the high-performing students are not gifted, though they may be more intelligent than average. While there is a positive correlation between intelligence and good grades at the high school level, work and commitment are very strong variables.
However, at the university level, there is a very strong positive correlation between the SAT scores and IQ scores. Those who perform very well on the SATs generally combine high intelligence with hard work. However, there are some highly intelligent students who do not perform well on the SAT’s and that softens the correlation between IQ and SAT scores. A student who is hard-working but whose IQ is close to average can often get high marks by selecting “softer” programs or attending colleges where standards are less rigorous.
