Now, even though there are limits to what IQ tests can tell you, they're widely
used and can be pretty useful especially for educators. The popularity of IQ
tests have been able to give us extensive knowledge of the range of IQ scores.
Let's look at what IQ scores look like for the entire population. IQ scores are
converted to have a mean of 100. Now the standard variation around the mean is
15 points. This standard variation is called the standard deviation. This show
how much the score varies from the mean. So, the mean would be 0 because
there's no difference. 15 points one way would be one standard deviation. Two
standard deviations and three standard deviations. Same with the other way. One
standard deviation from the mean, two standard deviations from the mean, and
three standard deviations from the mean. 68% of the population is within one
standard deviation from the mean. So 68% of the population has an IQ score
between 85 and a 115. Now, 95% of the population is within two standard
deviations from the mean. So 95% of the people you know score between 70 and a
130 on an IQ test, and 99.7% of the population scores within three standard
deviations of the mean. So between 55 and 145. Now, as you can see, with 99.7%
of the population scoring within three standard deviations in either direction
of the mean, that doesn't leave a lot of room for people to score above a 145
or below a 55. It's only about 15 out of 1,000 people score higher or lower
than either one of these two extremes. We also did an example like this in
lesson two, the research methods lesson. You should go back and check it out if
this is a little confusing. Now traditionally, those who have extreme IQ scores
are given labels. Such as a genius who scores above 140 on an IQ test because
not a lot of the population scores that high. Or intellectually disabled, those
who score less than 70 on the IQ test because again, not a lot of the
population score that low.
