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3.3 Graphics in the Media
LEARNING GOAL
Understand how to interpret the many types of more complex graphics that are commonly found in news media.
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Multiple Bar Graphs and Line Charts
A multiple bar graph is a simple extension of a regular bar graph: It has two or more sets of bars that allow comparison between
two or more data sets.
All the data sets must
have the same
categories so that
they can be displayed
on the same graph.
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Figure 3.18 A multiple bar graph. Source: Wall Street Journal Almanac.
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A multiple line chart follows the same basic idea as a multiple bar chart, but shows the related data sets with lines rather than bars.
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Figure 3.19 A multiple line chart. Source: New York Times.
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EXAMPLE 1 Reading the Investment Graph
Consider Figure 3.19 (previous slide). Suppose that, on July 7, you had invested $100 in a stock fund that tracks the S&P 500, $100 in a bond fund that follows the Lehman Index, and $100 in gold. If you sold all three funds on September 15, how much would you have gained or lost?
Solution: The graph shows that the $100 in the stock fund would have been worth about $105 on September 15. The $100 bond investment would have declined in value to about $99. The gold investment would have held its initial value of $100. On September 15, your complete portfolio would have been worth
$105 + $99 + $100 = $304
You would have gained $4 on your total investment of $300.
Pages Figure 3.19 is on the previous slide.
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EXAMPLE 2 Graphic Conversion
Figure 3.20 is a multiple bar graph of the numbers of U.S. households with computers and the number of on-line households.
Redraw this graph
as a multiple line
chart. Briefly
discuss the trends
shown on the
graphs.
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Figure 3.20 A multiple bar graph of trends in home computing. Source: Statistical Abstract of the United States.
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EXAMPLE 2 Graphic Conversion
Solution:
To convert the graphic to a multiple line chart, we must change the two sets of bars to a set of two lines. We place a dot corresponding to the height of each bar in the center of each category (year) and then connect the dots of the same color with a color-coded line, as shown in Figure 3.21.
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Figure 3.21 Multiple line chart showing the data from Figure 3.20.
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EXAMPLE 2 Graphic Conversion
Figure 3.21 Multiple line chart showing the data from Figure 3.20.
Solution: (cont.)
The most obvious trend is that both data sets show an increase with time. We see a second trend by comparing the bars within each year. In 1995, the number of on-line homes (about 10 million) was less than one-third the number of homes with computers (about 33 million).
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EXAMPLE 2 Graphic Conversion
Figure 3.21 Multiple line chart showing the data from Figure 3.20.
Solution: (cont.)
By 2003, the number of on-line homes (about 62 million) was about 90% of the number of homes with computers (about 70 million). This tells us that a higher percentage of computer users are going on-line. If we project the trends into the future, it seems likely that the number of on-line households will approach the number of households with computers, and both will approach the total number of households in the United States.
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Stack Plots
Another way to show two or more related data sets simultaneously is with a stack plot, which shows different data sets in a vertical stack.
Although data can be stacked in both bar charts and line charts, the latter are much more common.
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EXAMPLE 3 Stacked Line Chart
Figure 3.22 shows death rates (deaths per 100,000 people) for four diseases since Based on this graph, what was the death rate for cardiovascular disease in 1980? Discuss the general trends visible on this graph.
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Figure 3.22 A stack plot using stacked wedges. Sources: National Center for Health Statistics, American Cancer Society.
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EXAMPLE 3 Stacked Line Chart
Solution:
Each disease has its own color-coded region, or wedge; note the importance of the legend. The thickness of a wedge at a particular time tells us its value at that time.
For 1980, the cardiovascular wedge extends from about 180 to 620 on the vertical axis, so its thickness is about 440. This tells us that the death rate in 1980 for cardiovascular disease was about 440 deaths per 100,000 people.
The graph shows several important trends. First, the downward slope of the top wedge shows that the overall death rate from these four diseases decreased substantially, from nearly 800 deaths per 100,000 in 1900 to about 525 in The drastic decline in the thickness of the tuberculosis wedge shows that this disease was once a major killer, but has been nearly wiped out since 1950.
Meanwhile, the cancer wedge shows that the death rate from cancer rose steadily until the mid-1990s, but has dropped somewhat since then.
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Geographical Data
The energy use data in Table 3.3 are an example of geographical data, because the raw data correspond to different geographical locations.
Page 116 We used these data earlier to make a frequency table (Table 3.4), a histogram (Figure 3.8), and a stem-and-leaf plot (Figure 3.9).
Figure 3.23 Geographical data can be displayed with a color-coded map.
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TIME OUT TO THINK
What can you learn from the histogram in Figure 3.8 that you cannot learn easily from the geographical display in Figure 3.23? (Both are reproduced on the next slide.) What can you learn from the geographical display that you cannot learn from the histogram? Do you see any surprising geographical trends in Figure 3.23? Explain.
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Figure 3.23 Geographical data can be displayed with a color-coded map.
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Figure 3.24 shows a contour map of temperature over the United States at a particular time. Each of the contours (lines) connects locations with the same temperature. For example, the temperature is 50°F everywhere along the contour labeled 50° and 60°F everywhere along the contour labeled 60°.
Between these two contours,
the temperature is between
50°F and 60°F. Note that
greater temperature
differences mean more
tightly spaced contours.
For example, the closely
packed contours in the
northeast indicate that the
temperature varies sub-
stantially over small
distances.
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Figure 3.24 Geographical data that vary continuously, such as temperatures, can be displayed with a contour map.
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Three-Dimensional Graphics
Each of the three axes in Figure 3.27 carries distinct information, making the graph a true three-dimensional graph. Researchers studying migration patterns of a bird species (the Bobolink) counted the number of birds flying over seven New York cities throughout the night.
As shown on the inset map, the cities were aligned east-west so that the researchers would learn what parts of the state the birds flew over, and at what times of night, as they headed south for the winter. Notice that the three axes measure number of birds, time of night, and east-west location.
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Figure 3.27 This graph shows true three-dimensional data. Source: New York Times.
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Combination Graphics
EXAMPLE 6 Olympic Women
Describe three trends shown in Figure 3.28.
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Figure 3.28 Women in the Olympics. Source: Adapted from the New York Times.
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Solution
The line chart
shows that the
total number
of women
competing in
the summer
Olympics has
risen fairly
steadily,
especially since the 1960s, reaching nearly 5,000 in the 2004 games.
Figure 3.28 Women in the Olympics. Source: Adapted from
the New York Times.
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The pie charts show that the percentage of women among all competitors has also increased, reaching 44% in the 2004 games.
The bold red numbers at the bottom show that the number of events in which women compete has also increased dramatically, reaching 135 in the 2004 games.
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TIME OUT TO THINK
Which of the trends shown in Figure 3.28 are likely to continue over the next few Olympic games? Which are not? Explain.
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The End
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