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Normal Distributions

Many human variables fall on a normal or close to normal curve, including IQ, height, lifespan, and shoe size, to name only a few.

If extreme scores are omitted, income, number of children, housing costs, and eyesight would also be considered close to normal.

Because of this, we can estimate how many people will have a specific IQ, for example, just by knowing two things: the mean and the standard deviation.