Section 2.3 More Graphs for Quantitative Data 69 The result is shown in Figure 2.18. It is clear that the average declined from 2000 to 2002, generally increased from 2002 to 2007, dropped sharply in 2008, and increased in 2009. 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 14,000 12,000 10,000 8,000 6,000 4,000 2,000 0 Dow Jones Industrial Average ($) Dow Jones Industrial Average at the End of the Year Figure 2.18 Time-series plot for the Dow Jones Industrial Average Check Your Understanding 2. The Centers for Disease Control and Prevention surveyed U.S. high school students every two years to determine the percentage who said they had used marijuana one or more times. The following time-series plot presents the results. 1991 1993 1995 1997 1999 2001 2003 2005 2007 50 40 30 20 10 0 Percent Percentage of High School Students Using Marijuana a. During what time period was marijuana use among high school students the highest? b. True or false: At one time, more than half of all high school students reported using marijuana. c. During what periods of time was marijuana use increasing? During what periods of time was it decreasing? d. True or false: Marijuana use among high school students in 2007 was lower than it had been since 1991. Answers are on page 74.
navidi_monk_essential_statistics_1e_ch1_3
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