GRAPHICAL DESCRIPTIVE STATISTICS FOR QUALITATIVE, TIME SERIES AND RELATIONAL DATA

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• GRAPHICAL DESCRIPTIVE STATISTICS FOR QUALITATIVE,
  TIME SERIES AND RELATIONAL DATA

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Reasons To Collect Data

• Obtain Input to a Research Study
• Measure Performance
• Assist in Formulating Decision Alternatives
• Satisfy Curiosity
• Knowledge for the Sake of Knowledge

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Random Variables

• Random variables are phenomena or characteristics
  that are not known in advance
• Data are observations of random variables

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TYPES OF DATA

• Qualitative
• Result to a survey question is non-numeric
• Categorical Data
• Ordinal (Ranked) Data
• Quantitative
• Result to a survey question is a number
• Ratio Data Has an absolute 0 point, e.g. age
• Interval 0 is simply another number e.g.
  degrees Fahrenheit

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Graphical TechniquesQualitative Data

• Pie Charts
• Bar Charts

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Plot of Frequency Distributions

• Objective is to develop a frequency distribution
  table
• Hand Count
• Excel Approach
• COUNTIF command

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Pie Charts

• Determine the relative frequency for each
  category
• Apportion sectors (wedges) of a 360 degree circle
  proportionately

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Example

• Frequency Distribution of Origin of Car
  Manufacturer

Frequency American 16 Asian 20 European
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Relative Frequency .40 .50 .10
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Pie Chart
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Bar Charts

• Bars show the frequency or relative frequency of
  the observations
• Consider the same example

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Frequency Bar Chart
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Relative Frequency Bar Chart
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EXCELPie Charts

• Example -- 66 people surveyed and asked the color
  of their car -- Their choices
• Red
• Blue
• Black
• White
• Other
• These are recorded in cells A2 to A67 of a
  spreadsheet

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Determining Frequency DistributionsStep 1
Record Responses in a Column
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Step 2 Type Categories in another Column
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Step 3 Use COUNTIF to Determine Frequencies
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Creating a Pie Chart
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Creating a Pie Chart - 2
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Creating a Pie Chart - 3
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Creating a Pie Chart - 4
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Creating a Pie Chart - 5
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Completed Pie Chart
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Editing Options

• Enlarge
• Put Labels Inside Wedges
• Change Colors
• Add Text
• Etc.

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EXCELBar Charts

• What we call Bar Charts, Excel calls Column
  Charts
• The steps are similar
• If you already have a pie chart, you can convert
  it to a bar chart as shown on the next slide

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Creating a Bar Chart From a Pie Chart
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Resulting Bar Chart
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Line Charts for Time Series Data

• Time series -- Values vs. time
• Dow Jones vs. Day
• Sales vs. Quarter
• Population vs. Year
• Typically depicted as line charts
• In Excel if you already have a bar chart you can
  convert it to a line chart using the method on
  the last slide
• Otherwise we do the following

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Example -- Sales at Epencil.com
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Note In this dialogue box, there are many
editing features
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Can now edit figure Resize Delete Gray
Background Delete Lines Etc.
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Scatter Diagrams -- Showing Relationships
Between Variables

• A scatter diagram shows the relationship between
  two quantitative variables as a plot of a series
  of points (observations)
• (Grade vs. Study time)
• (Sales vs. Advertising )
• (Production vs. Resources)
• Types of relations that can be detected
• Linear (Positive or Negative)
• Least Squares Line -- Best line through points
• Nonlinear
• No Relation

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Example

• Sales of Pencils at Epencil vs. Advertising
  spent during the week

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In this dialogue box there are many editing
features
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Can now edit figure Resize Delete Gray
Background Delete Lines Etc.
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Determining Trend

• We can have Excel put the best straight line or
  other curve (parabola, etc.) through these points
  so that we can easily observe trend

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2. Select Add Trendline from the Popup Menu
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How to Lie With Statistics

• Graphs can be used to accurately portray data
• However, sometimes a graph can be distorted in
  such a way as to skew the information it conveys
• Examples
• Fatter or different shaped bars
• Stretched or condensed axes
• No indication of a break on the axis
• Unlabeled axes

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Review

• How to construct by hand and by Excel
• Pie Charts for Qualitative Data
• Bar Charts for Qualitative Data
• Line Charts for Time Series Data
• Scatter Diagrams to Show Relationships Between
  Variables
• How Graphs Can be Deceptive