Graphs, Good and Bad

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Chapter 10

• Graphs, Good and Bad

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Thought Question 1
What is confusing or misleading about the
following graph?
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Distribution

• Tells what values a variable takes and how often
  it takes these values
• Can be a table, graph, or function

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Variables

• Categorical
• Places an individual into one of several groups
  or categories
• Display distribution with a bar graph or a pie
  chart
• Quantitative (Numerical)
• Takes numerical values for which arithmetic
  operations such as adding and averaging make sense

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Case Study (from Ch.1)
The Effect of Hypnosis on the Immune System

• Easy or difficult to achieve hypnotic trance
• Group assignment
• Pre-study white blood cell count
• Post-study white blood cell count

categorical quantitative
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Case Study (from Ch.1)
Weight Gain Spells Heart Risk for Women

• Age (in 1976)
• Weight in 1976
• Weight at age 18
• Incidence of coronary heart disease
• Other smoking, family history, menopausal
  status, post-menopausal hormone use.

quantitative
categorical
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Class Make-up on First Day(Summer 2002)
Data Table
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Class Make-up on First Day(Summer 2002)
Pie Chart
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Class Make-up on First Day(Summer 2002)
Bar Graph
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Line Graphs

• A line graph shows behavior over time.
• Time is always on the horizontal axis.
• Look for an overall pattern (trend).
• Look for patterns that repeat at known regular
  intervals (seasonal variations).
• Look for any striking deviations that might
  indicate unusual occurrences.

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Class Make-up on First Day(Fall Semesters
1985-1993)
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Beware of Pictograms
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Another Misleading Graph
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Making Good Graphs

• Title your graph.
• Make sure labels and legends describe variables
  and their measurement units. Be careful with the
  scales used.
• Make the data stand out. Avoid distracting
  grids, artwork, etc.
• Pay attention to what the eye sees. Avoid
  pictograms and tacky effects.

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Key Concepts

• Categorical and Quantitative Variables
• Distributions
• Pie Charts
• Bar Graphs
• Line Graphs
• Techniques for Making Good Graphs