Section_1_3 - Sec 1.3 Density Curves and Normal...

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Sec 1.3 - Density Curves and Normal Distributions Recall : A histogram can be made by setting the height of the bars equal to the actual count of a class or by setting it equal to the percent of that class with respect to the data total. Using percents, if we set the width of the bars equal to one, then the total area of the bars must be 1 (because the bars must add up to 100%). I.Density Curves: a smooth approximation to a histogram Definition : A density curve is a curve that: i) is always on or above the horizontal axis ii) has area exactly 1 underneath it a smooth approximation to a histogram. A density curve describes the overall pattern of a distribution. The area under the curve between two values on the horizontal axis gives the percent of the data that falls within that range of data. The quartiles can be estimated using a density curve. The median is the point at which half the area under the curve lies to the right and half to the left. The first quartile has ¼ the area to the left, and the third quartile has ¾ of the area to the left.
The mean and standard deviation are more difficult to find. The mean is the point at which the density curve would balance if it were made out of a solid material.

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