CHAPTER 3 Measures of Central Tendency distribute or post, © iStockphoto.com/SolStock Introduction copy, Education and Central Averages and Energy Consumption Tendency Definitions of Mode, Median, and Mean Central Tendency, Education, Calculating Measures of Central and Your Health Tendency With Raw Data Income and Central Tendency: Calculatingnot Measures of Central The Effect of Outliers Tendency With Grouped Data Chapter Summary Do Copyright ©2020 by SAGE Publications, Inc. 81 This work may not be reproduced or distributed in any form or by any means without express written permission of the publisher. 82 Statistics and Data Analysis for Social Science INTRODUCTION How much income does the typical American take home each year? Are SAT math Measures of central scores higher since the implementation of the No Child Left Behind act? Is the typi- tendency: A cal level of education higher for males than for females? These kinds of questions group of are addressed using a group of statistics known as measures of central tendency. statistics that indicate where The most commonly known of these is the mean, or average. Others include the cases tend to mode and the median. They tell us what is typical of a distribution of cases. In other cluster in a words, they describe where most cases in a distribution are located. distribution or what is In this chapter, we learn the three most commonly used measures of central typical in a tendency: the mode, the median, and the mean (Table 3.1). Pay particular attention distribution. The to the circumstances in which each one is used, what each of them tells us, and how most common measures of each one is interpreted. We also learn how to calculate each of these measures with central tendency both raw data and grouped data (data in frequency tables). are the mode, median, and mean. AVERAGES AND ENERGY CONSUMPTION Averages are one of the most commonly used statistics we encounter on a daily basis. Average: A statistic that Among a myriad of other items, averages are used to describe the weather, gas mileage represents what in our cars, stock market performance, and our weekly expenditures. Likedistribute all statis- is typical in a tics, averages allow us to summarize, describe, and predict events in our daily lives. distribution. You probably learned how to calculate an average many years ago, so it may seem quite simple. It is just one of three commonly used measuresor of central tendency that describe what is typical about data; surprisingly, it is the complicated one of the TABLE 3.1 Symbol Meaning of Symbolpost, Formula Measures of A group of statistics (mode, median, and mean) central tendency that are used to describe where cases tend to fall in a distribution. They tell us what is typical in a distribution. Mode (Mo) The most frequently occurring value or attribute Median (Md) The value of the middle case in a rank-ordered copy,distribution The mathematical average for sample data ()X ∑ X Mean X = N notMean (σ) The mathematical average for population data σ σ = x N Position of the Formula used to determine which case number (in a N + 1 Do median rank-ordered distribution of cases) is the median 2 Outliers Cases with very high or very low values Copyright ©2020 by SAGE Publications, Inc. This work may not be reproduced or distributed in any form or by any means without express written permission of the publisher. ChaptER 3 Measures of Central Tendency 83 three. In statistics, the mathematical average is referred to as the mean. The other two commonly used measures of central tendency are the mode and the median. Each of these three measures can tell us what is typical about a distribution of cases; taken together, they tell us even more. Each represents a unique description of the values around which cases tend to cluster (hence the term central tendency). Averages can be found in all walks of life, but they are particularly common in the world of sports. For example, a person watching a professional football game is likely to encounter the following averages: yards gained per game, yards allowed per game, yards per play, yards per carry, yards per throw, yards per catch, yards per kickoff return, yards per punt return, and hang time of punts. Other more obscure aver- ages are also increasingly common, for example, average number of passing yards after halftime during a snowstorm game in December while wearing Adidas shoes (just kidding, although it is possible that Adidas marketers have looked into this). Statistically, these are referred to as means, but we tend to call them averages. Other “hidden” averages that we often do not think of as averages include the following: winning percentage, pass completion percentage, and field goal percent- age. Baseball, basketball, hockey, and other sports provide viewers with a plethora of statistical averages that consumers can use to reify their sports viewing expe- rience by using them to draft fantasy teams, bet on events, and talk sports with friends. Like all statistics, we tend to use these averages to summarize, describe, and predict the outcome of sporting events and individual performances. In fact,distribute sports may be the social institution most responsible for single-handedly popu- larizing statistics among the American public. This chapter discusses these three statistics—mode, median, and mean—and demonstrates the advantages and draw- backs of each using a variety of examples. or The distribution of cases across the attributes of any variable can be described using a variety of statistics. The three most commonly used measures of central tendency are the mode, median, and mean. Each is based on a distinct logic, but all three are used for the same general purpose: They tell us where in a distribution the cases tend to cluster. post, copy, not Do © iStockphoto.com/JMichl Copyright ©2020 by SAGE Publications, Inc. This work may not be reproduced or distributed in any form or by any means without express written permission of the publisher. 84 Statistics and Data Analysis for Social Science The mode, median, and mean cannot be used interchangeably. Each tells us something different. The mode tells us which attribute has the greatest frequency. The median tells us the value of the case that divides the distribution into two equal- sized parts, one part containing cases with greater values and the other part contain- ing cases with lesser values. The mean tells us the arithmetic average of the cases. It is important to understand that certain measures of central tendency apply to only certain types of variables. When working with nominal variables, only the mode can be used. When working with ordinal variables, only the mode and median can be used. When working with interval/ratio variables, all three measures can be used. See Table 3.2 for a summary of when different measures can be used. On October 12, 2006, the U.S. Bureau of the Census announced that the population of the United States would reach 300 million people on October 17, 2006, at about 7:46 a.m. Eastern Daylight Time. Of course, nobody really knew the exact moment when the population reached this historic milestone, but at some point during mid-October 2006, it is highly likely that somebody became the 300 millionth live American (as of 2018, the U.S. population was about 326 million). As only the fourth society in the his- tory of the world to reach this milestone, it puts the United States in the same company as China, India, and the former Soviet Union. To put this number in perspective, it would take the combined populations of present-day Germany (83 million), France (68 million), Italy (61 million), Spain (47 million), Poland (38 million), and Republic of Ireland (5 million) to surpass the population of the United States in 2006.distribute Population has been a popular topic for social analysts, city planners, and environ- mentalists for thousands of years. As the world population grew into the 19th century, the work of the Reverend Thomas Malthus (1766–1834) took on greater significance. Malthus (1798/1993) argued that because population grows exponentiallyor while food production grows linearly, the day will come when hunger and starvation become unavoidable aspects of life on Earth. He also argued that a series of preventive checks, such as delayed marriage and abstinence, would help to avoid or at least minimize the problems associated with food shortages. While some analysts still adhere to varia- tions on Malthus’s ideas, others claim that nutrition and starvation have economic, political, and technological dimensions that Malthus did not consider. Nevertheless, in the current model post,of development, with population growth come increases in energy consumption. History shows that the more people there are, the more energy they consume. The question is, how big of an increase in energy con- sumption accompanies the increases in population growth? A comparison of total primary energy consumption (petroleum, dry natural gas, coal, nuclear, hydroelec- tric, and nonhydroelectric renewable) across countries helps to answer this ques- tion. Accordingcopy, to the U.S. Energy Information Administration’s international data TABLE 3.2 not Nominal Ordinal Interval/Ratio Mode Applies Applies Applies Median NA Applies Applies Do Mean NA NA Applies Note: NA, not applicable. Copyright ©2020 by SAGE Publications, Inc. This work may not be reproduced or distributed in any form or by any means without express written permission of the publisher. ChaptER 3 Measures of Central Tendency 85 © iStockphoto.com/xavierarnau distribute browser (https://www.eia.gov/beta/international/analysis.php), the U.S. population, which in 2003 was just under 300 million people, consumed a total of 103.3 exajoules (EJ) of energy (1 EJ = 1018 joules [power]).