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Chapter 3: Displaying and Describing Categorical Data*Data Analysis
*Frequency Tables, Bar Charts, Pie Charts Contingency Tables
Titanic Who: People on the Titanic
What: survival status, age, sex, ticket class
When: April 14, 1912
Where: North Atlantic
How: A variety of sources and internet sites
Why: Historical interest
Data Analysis Rule #1: Make a picture
a display of your data will revewal thins you are not likely to see in a table of numbers and will help you THINK clearly about the patterns and relationships that may be hiding in your data
Rule # 2: Make a picture A well-designed display will SHOW the important features
and patterns in your data. A picture will also show you the things you did not expect to see: the extraordinary (possibly wrong) data values or unexpected patterns
Rule # 3: Make a picture The best way to TELL others about our data is with a well-
chosen picture.
Picking a Display Determine if your variable is categorical or quantitative
If categorical: frequency tables bar charts pie charts contingency tables
If quantitative: wait till next chapter!
Frequency Tables records the totals and the category names
Example:
Class Count
First 325
Second 285
Third 706
Crew 885
Relative Frequency Table
displays the percentages and category names
Example:
Class %
First 14.77
Second 12.95
Third 32.08
Crew 40.21
Proportion: the fraction of data in each category
(divide the counts by the total number of cases)
Relative = Percent
Bar Charts Displays the distribution of a categorical variable,
showing the counts for each category next to each other for easy comparison.
Bars should be the same width Bars should have spaces between them Axis should both be labeled with a title and/or scale
Pie Charts shows the whole group of cases as a circle. They slice the
circle into pieces whose size is proportional to the fractions of the whole in each category.
Categorical Data Condition The data are counts or percentages of individuals in
categories.
Before you make a pie chart or a bar graph you must check this condition!!!