64 CHAPTER 2 Exploring Data with Tables and Graphs Bar Graphs A bar graph uses bars of equal width to show frequencies of categories of categorical (or qualitative) data. The bars may or may not be separated by small gaps. Feature of a Bar Graph ■ Shows the relative distribution of categorical data so that it is easier to compare the different categories Pareto Charts A Pareto chart is a bar graph for categorical data, with the added stipulation that the bars are arranged in descending order according to frequencies, so the bars decrease in height from left to right. Features of a Pareto Chart ■ Shows the relative distribution of categorical data so that it is easier to compare the different categories ■ Draws attention to the more important categories Time-Series Graph of Global PC Shipments EXAMPLE 3 The time-series graph shown in Figure 2-7 depicts the yearly number (millions) of PC computers that were shipped. See that shipments rose steadily until 2011 when they reached a peak and began to decline. Ignoring such important trends could be catastrophic for businesses trying to remain competitive. YOUR TURN. Do Exercise 9 “Gender Pay Gap.” FIGURE 2-7 Time-Series Graph of Global PC Shipments Pareto Chart of Causes of Fatal Plane Crashes EXAMPLE 4 Example 2 in Section 2-1 included a frequency distribution describing the causes of fatal plane crashes. Figure 2-8 shows the Pareto chart based on Table 2-3 in that example. Figure 2-8 and Table 2-3 contain the same basic data, but Figure 2-8 is a graph that allows for better understanding the data. Note that Figure 2-8 draws attention to the fact that pilot error is by far the most serious cause of fatal plane crashes. Note also that Figure 2-8 does not strictly follow the requirement that the heights of the bars decrease from left to right, but it makes sense to locate the category of “other” at the far right part of the graph. Florence Nightingale Florence Nightingale (1820–1910) is known to many as the founder of the nursing profession, but she also saved thousands of lives by using statistics. When she encountered an unsanitary and undersupplied hospital, she improved those conditions and then used statistics to convince others of the need for more widespread medical reform. She developed original graphs to illustrate that during the Crimean War, more soldiers died as a result of unsanitary conditions than were killed in combat. Florence Nightingale pioneered the use of social statistics as well as graphics techniques. ( a o
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