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## Graphs, Good and Bad

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**Graphs, Good and Bad**MA155 Chapter 10**Organizing Data**• The first step in data analysis is to display the data in a graph. • Look first for the overall pattern in the data, and then for striking exceptions to that pattern. • After looking at the graphs, you can use well-chosen numerical descriptions.**Describing Distributions**• Distributions • The distribution of a variable tells us what value the variable takes and how often each value occurs.**Data Tables**• Clearly Labeled • Units are stated • Source of Data**Pie Charts**• A whole is divided into parts • Steps • Draw a circle • Make wedges that are representative of the proportion • The parts do make a whole**Bar Graph**• The height of each bar shows the proportion • It clearly shows the results • They are easy to make**Categorical Variable**Places an individual into one of several groups or categories Quantitative Variable Takes numerical values for which arithmetic operations make sense Types of Variables**Categorical Examples**• Race • Sex • Employment Status • Hair Color • Type of Car**Quantitative Examples**• Measurements made on scales of equal units • Examples • Height in inches • Reaction time in seconds • Temperature in degrees Celsius**Remember**• Not all numbers carry the same information • Luke is a skateboarder. • Luke finished first at the 2000 Gravity Games • Luke scored a 92.60 on the street course. • The scale of measurement depends on the measuring process, not on the property measured.**Displaying Distributions**• To display the distribution of a variable measured in a nominal scale, use a pie chart or a bar graph • Pie charts emphasize how individual counts or percents are related to the whole • Bar graphs emphasize how quantities compare with one another. • Use pie charts and bar graphs when displaying the distribution of categorical variables.**Pictograms**Source: http://www.usatoday.com**Line Graphs**• Show the behavior of a variable over time • Horizontal Axis Time • Vertical Axis Scale of Variable**Scales**• The scales of a line graph can cause a graph to be misleading**Making Good Graphs**• Must be clearly labeled • Units stated • Source of Data • Make the data stand out!**Homework**• Read Chapter 11 • Suggested Problems: • 10.1, 10.3, 10.9, 10.13, 10.17, 10.27