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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.

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Graphs, Good and Bad

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Graphs good and bad l.jpg

Graphs, Good and Bad

MA155

Chapter 10


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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.


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Describing Distributions

  • Distributions

  • The distribution of a variable tells us what value the variable takes and how often each value occurs.


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Data Tables

  • Clearly Labeled

  • Units are stated

  • Source of Data


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Eye Color of Students


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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


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Pie Graph


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Bar Graph

  • The height of each bar shows the proportion

  • It clearly shows the results

  • They are easy to make


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Bar Graph


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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


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Categorical Examples

  • Race

  • Sex

  • Employment Status

  • Hair Color

  • Type of Car


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Quantitative Examples

  • Measurements made on scales of equal units

  • Examples

    • Height in inches

    • Reaction time in seconds

    • Temperature in degrees Celsius


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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.


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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.


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Pictograms

Source: http://www.usatoday.com


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Line Graphs

  • Show the behavior of a variable over time

  • Horizontal Axis Time

  • Vertical AxisScale of Variable


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Scales

  • The scales of a line graph can cause a graph to be misleading


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Making Good Graphs

  • Must be clearly labeled

  • Units stated

  • Source of Data

  • Make the data stand out!


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Homework

  • Read Chapter 11

  • Suggested Problems:

  • 10.1, 10.3, 10.9, 10.13, 10.17, 10.27


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