Percentage Pie Charts

What Is It Good For?

Pie charts show relationships between parts of a whole or percentages as pieces of a pie. These help display data so publics and decisionmakers can quickly determine what is significant. For example, readers can see the proportion of items within a budget or how much time and money are spent on each category or the breakdown of responses to a survey question. They can answer questions such as:

 
• Did Reclamation spend more money on construction or operation in 1997, and how does this compare with the way money was spent in 1970?
• What are power users' primary concerns and issues, and how does this compare with environmental groups' concerns.

How Do I Use It?

Use one pie chart for each idea, such as a survey question, expenditures for a year, or water demands for a month in a given area. Then list all of the factors or elements involved in that idea (e.g., responses to a survey question, dollars in a budget item). Divide a circle into pieces of pie. Each piece will represent the percentage that particular element received.

You might want to compare pie charts to examine various elements. Sometimes, small issues may be responsible for a large part of the problem. See Pareto Chart.

Pie charts can be generated for different points in time or for various scenarios to show proportional differences--for example the distribution of employment among 10 economic sectors in the years 1990, 2000, and 2010.

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