ch4_outline

# ch4_outline - Chapter 4 Outline Introduction We continue...

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Chapter 4 Outline Introduction We continue our study of descriptive statistics with measures of dispersion, such as dot plots, stem and leaf displays, quartiles, percentiles, and box plots. Dot plots, a stem-and-leaf display, and box plots give additional insight into where the values are concentrated and dispersed and the general shape of the data. Finally we consider bivariate data where we observe two variables for each individual or observation selected. Dot Plots In Chapter 2 we grouped data in classes and constructed a histogram. When we organize the data into classes, we lose the exact value of the observations. Dot plots group data as little as possible, hence we do not lose the identity of the individual observations. Dot Plot : A graph for displaying a set of data. Each numerical value is represented by a dot placed above a horizontal number line. To develop a dot plot we display a dot for each observation along a horizontal number line indicating the value of each piece of data. For multiple observations we pile the dots on top of each other. The steps to follow in developing a dot plot graph are: 1. Sort the data from smallest to largest. 2. Draw and label a number line. 3. Place a dot for each observation. As an example, the lengths of service, in years, of a sample of eighteen employees are given. Step 1: Sort the data from smallest to largest. 2 3 3 4 4 5 5 5 6 6 6 6 7 7 7 8 8 10 Step 2: Draw the number line and label it as shown. 0 2 4 6 8 10 12 Step 3: Place a dot for each observation. 0 2 4 6 8 10 12 Length of Service (in years) 7 6 2 10 6 6 5 8 4 8 4 7 6 5 3 3 7 5

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Other Measures of Dispersion The standard deviation is the most widely used measure of dispersion. However there are other methods for describing the variation in a data set. One method is to determine the values in a data set that divide the data into equal parts. These values include quartiles , deciles , and percentiles . Quartiles Recall that the median divides data that has been placed in order from smallest to largest, such that half the values are below the median and half are above the median. If we divide the lower and upper set of values into two equal parts, we have quartiles. Quartiles divide a set of data into four equal parts.
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ch4_outline - Chapter 4 Outline Introduction We continue...

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