Probability and Statistics > Basic Graphs and Charts > Pie Chart

## What is a Pie Chart?

A Pie Chart is a type of graph that displays data in a circular graph. The pieces of the graph are proportional to the fraction of the whole in each category. In other words,** each slice of the pie is relative to the size of that category** in the group as a whole. The following chart shows water usage (image courtesy of the EPA).

Pie charts give you a snapshot of how a **group** is broken down into **smaller pieces**. The following chart shows what New Yorkers throw in their trash cans. You could read that New Yorkers (perhaps surprisingly) throw a lot of recyclables into their trash, but a pie graph gives a clear picture of the large percentage of recyclables that find their way into the trash.

In order to make a pie chart, you must have a list of **categorical variables** (descriptions of your categories) as well as **numerical variables**. In the above graph, percentages are the numerical variables and the type of trash are the categorical variables.

While it’s possible to draw one by hand, it isn’t really necessary with the wide variety of computer programs that can make pie charts for you. Two of the most popular programs for making charts in elementary statistics or AP statistics classes are **Microsoft Excel** and **IBM SPSS Statistics**:

Pie chart in Excel.

Pie chart in IBM SPSS Statistics.

**Note:** When you make a pie chart, you must make sure that your categories don’t overlap, otherwise you’ll have a meaningless chart. For example, if you have a chart of what breeds of dog U.S. pet owners own, you can’t put a husky-German shepherd mix in two categories, otherwise it will create larger pieces of the “pie” for those categories.

**Reference**:

What’s in NYC’s Waste? Retrieved February 2, 2016 from: http://www.nyc.gov/html/nycwasteless/html/resources/wcs_charts.shtml

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