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There are two uses of pie graphs.
First, a graph for displaying the relative frequency distribution of a category variable in which a circle is divided into sectors, representing categories, so that the area of each sector represents the relative frequency of values in the category. See Example 1 below.
Second, a graph for displaying bivariate data; one category variable and one numerical variable. A circle is divided into sectors, representing categories, so that the area of each sector represents the value of the numerical variable for the sector as a percentage of the total value for all sectors. See Example 2 below.
For categories that do not have a natural ordering, it is desirable to order the categories from the largest sector area to the smallest.
Example 1
Students enrolled in an introductory Statistics course at the University of Auckland were asked to complete an online questionnaire. One of the questions asked them to enter their ethnicity. They chose from the following list: Chinese, Indian, Korean, Maori, New Zealand European, Other European, Pacific, Other. The 727 responses are displayed on the pie graph below.
Example 2
World gold mine production for 2003 by country, based on official exports, is displayed on the bar graph below.
Alternatives: circle graph, pie chart
Curriculum achievement objectives references
Statistical investigation: Levels (4), (5), (6), (7), (8)
