Pie Charts

Circle graphs, or pie charts, represent data as sections of the circle (or “pieces of the pie”), corresponding to their percentage of the whole. Circle graphs are often used to show how a whole set of data is broken down into individual components.

Here’s an example: At the beginning of a semester, a teacher talks about how she will determine student grades. She says, “Half your grade will be based on the final exam, and [latex]20\%[/latex] will be determined by quizzes. A class project will also be worth [latex]20\%[/latex] and class participation will count for [latex]10\%[/latex].” In addition to telling the class this information, she could also create a circle graph.

This graph is useful because it relates each part—the final exam, the quizzes, the class project, and the class participation—to the whole.

In the following video, an example of using a pie chart to determine a percent of a whole is shown.

Bar Graphs

Bar graphs are another way to represent categorical data graphically. The bar graph below represents the distribution of students at a four-year college categorized by class standing. 31% of students are freshmen, 16% are sophomores, 27% are juniors, and 26% are seniors. In a bar graph, the height of each bar corresponds to the percent, or relative frequency, of data values observed in each category.