ch03 - blu03683_ch03.qxd 09/08/2005 01:05 PM Page 95 CHAPTE...

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3–1 Objectives After completing this chapter, you should be able to 1 Summarize data using measures of central tendency, such as the mean, median, mode, and midrange. 2 Describe data using measures of variation, such as the range, variance, and standard deviation. 3 Identify the position of a data value in a data set, using various measures of position, such as percentiles, deciles, and quartiles. 4 Use the techniques of exploratory data analysis, including boxplots and Fve-number summaries, to discover various aspects of data. Outline 3–1 Introduction 3–2 Measures of Central Tendency 3–3 Measures of Variation 3–4 Measures of Position 3–5 Exploratory Data Analysis 3–6 Summary 3 3 Data Description CHAPTER
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96 Chapter 3 Data Description 3–2 Statistics Today How Long Are You Delayed by Road Congestion? No matter where you live, at one time or another, you have been stuck in trafFc. To see whether there are more trafFc delays in some cities than in others, statisticians make comparisons using descriptive statistics. A statistical study by the Texas Transportation Institute found that a driver is delayed by road congestion an average of 36 hours per year. To see how selected cities compare to this average, see Statistics Today—Revisited at the end of the chapter. This chapter will show you how to obtain and interpret descriptive statistics such as measures of average, measures of variation, and measures of position. 3–1 Introduction Chapter 2 showed how one can gain useful information from raw data by organizing them into a frequency distribution and then presenting the data by using various graphs. This chapter shows the statistical methods that can be used to summarize data. The most familiar of these methods is the Fnding of averages. ±or example, one may read that the average speed of a car crossing midtown Manhattan during the day is 5.3 miles per hour or that the average number of minutes an American father of a 4-year-old spends alone with his child each day is 42. 1 1 “Harper’s Index,” Harper’s magazine.
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In the book American Averages by Mike Feinsilber and William B. Meed, the au- thors state: “Average” when you stop to think of it is a funny concept. Although it describes all of us it describes none of us. . . . While none of us wants to be the average American, we all want to know about him or her. The authors go on to give examples of averages: The average American man is Fve feet, nine inches tall; the average woman is Fve feet, 3.6 inches. The average American is sick in bed seven days a year missing Fve days of work. On the average day, 24 million people receive animal bites. By his or her 70th birthday, the average American will have eaten 14 steers, 1050 chickens, 3.5 lambs, and 25.2 hogs.
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ch03 - blu03683_ch03.qxd 09/08/2005 01:05 PM Page 95 CHAPTE...

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