FRAME 52.

Notice the curve has two horizontal scales; one measured in meals/day and the other

measured in standard deviations from the mean. The distance 2000 to 2200 is the same as the

distance u to u +2σ A special relationship exists between the area under the normal curve and

the horizontal distance from the mean measured in standard deviations.

This relationship is the sixth characteristic of a normal curve and is commonly referred to as

the Empirical rule.

The rule states that: a) the area under the normal curve from u -a to u + σ is approximately

68% of the total area under the curve. b) the area under the normal curve from u -2σ to u + 2σ

is approximately 95%. c) the area under the normal curve from u -3σ to u + 3σ is

approximately 99.7%.

The following diagram illustrates this Empirical rule:

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