Educational Psychology / Unit 8 EDP 0715 worked example, 60 to 90 seconds
IQ on the Normal Curve
The idea
IQ scores follow a normal distribution, the symmetrical bell-shaped curve, with a mean of one hundred and a standard deviation of fifteen. Most people score near the middle, and scores become rarer the farther they lie from it. About two percent of people score above 130, two standard deviations above the mean, and about two percent below 70, two standard deviations below. Reading a score means asking how many standard deviations it lies from the mean.
In practice
Worked example: a score of 115 lies one standard deviation above the mean. A score of 130 lies two above it, higher than about 98 percent of same-age peers. A score of 85 lies one standard deviation below the mean.
Where people slip
A score of 130 is two standard deviations above the mean, not two percent above it; the two percent refers to how many people score higher. Statistics for reading these curves return in unit twelve.
Your place on the trail
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