Topic 1: Organizing Information Pictorially Using Charts and Graphs

A picture is worth N words, where N is large.

Graphs and charts can show patterns which are difficult to see in raw data.

A variable is a characteristic of an object or a person, that can change from one object or person to the next.

Example:

A person is sometimes referred to as an individual or a case.

Variables assigned numeric values are quantitative, and those assigned a category are categorical.

A bar graph and a pie chart are two ways of representing categorical variables pictorially.

(Note: graph and chart are often used interchangeably)

• charts and graphs can represent categorical variables
  OR
  they can represent quantitative variables when the values fall in a few groupings or classes
  
• labels should be used, but be careful of "clutter"
  
• decide first on groupings, then determine the number of cases in each
  
• height in a bar chart can be numeric total or proportion of percentage
  
• pie charts are useful to show the percentage of whole for each category

From USA Today, Feb. 17, 2000

Note in the bar chart above how the classes above are not a uniform size. Contrast this to a histogram.