Chapter 3 Displaying and Describing Categorical Data

Graphs for Categorical Data

Bar Graph 4 Used for categorical data 4 Bars do not touch 4 Categorical variable is typically on the x-axis and numerical values on the y-axis 4 To describe – comment on which occurred the most often or least often 4 May make a double bar graph or segmented bar graph for bivariate categorical data sets

Example: spam is the curse of the Internet. Here is a compilation of the most common types of spam. Type of SpamPercent Adult19 Financial20 Health7 Internet7 Leisure6 Products25 Scams9 Other?

a) What percent of spam would fall in the “Other” category? b) Display these data in a bar graph. Be sure to label your axes and title your graph.

Segmented Bar Charts A segmented bar chart displays the same information as a pie chart, but in the form of bars instead of circles. Each bar is treated as the “whole” and is divided proportionally into segments corresponding o the percentage in each group. Here is the segmented bar chart for ticket Class by Survival status:

Pie (Circle) Graph 4 Used for categorical data 4 To make: –Proportion (part/whole) 360° –Using a protractor, mark off each part 4 Must include all the categories that make up a whole 4 Used when you want to emphasize each category’s relation to the whole. 4 To describe – comment on which occurred the most often or least often

Grape Production 4 Create a Pie Graph: 4 The 1998 Grape Crush Report for San Luis Obispo and Santa Barbara counties in California gave the following information on grape production for each of seven different types of grams (Peck 2008: San Luis Obispo Tribune, February 12, 1999): Type of GrapeTons Produced Cabernet Sauvignon 21,656 Chardonnay39,582 Chenin Blanc1,601 Merlot11,210 Pinot Noir2,856 Sauvignon Blanc5,868 Zinfandel7,330 TOTAL90,103