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: ClassCount First325 Second285 Third706 Crew885

Relative Frequency Table  displays the percentages and category names  Example: Class% First14.77 Second12.95 Third32.08 Crew40.21 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!!!