Chapter 2: Summarizing and Visualizing Data

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JoVE Core
Statistica

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JoVE Core Statistica

Pie Chart

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Consider a table that summarizes the occurrence of COVID-19 cases in different countries. Such qualitative data with the frequency counts can be represented using the Pie chart, a graph in the form of a circle, just like a pie. So, how is the data from a table converted into a pie chart? First, divide the number of COVID cases in country A by the sum of all the COVID cases. Multiply this value by 360 degrees—the degrees in a full circle—to get the sector angle of the corresponding country. Similarly, calculate the sector angles for the other countries. Using these sector angles, divide the circle into slices equivalent to the given number of categories. Notice that the percentage frequencies of COVID cases also correspond to the size of their slices. Here, country E, with the largest sector, indicates the highest percentage of COVID cases. In contrast, country F, with the smallest sector angle, shows the least percentage of cases.

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A pie chart (or a pie graph) is a circular graphical chart or a pictorial representation of categorical data. It is divided into slices of pie each indicating numerical proportions. It is also used to show the relative sizes of data in a single chart.

In a pie chart, the central angle, the arc length of each slice, and the area are directly proportional to the quantity or percentage it represents. Some real-world examples that can be depicted using pie charts include marks obtained by students in a class, the monthly expenditure of a family, and the cost of construction of a house. With the help of a pie chart, one can easily compare the sum spent on steel, cement, and so on during construction. The actual sum spent on each individual expense can also be computed.

A pie chart's main advantages are that it is simple to use and easy for the audience to quickly analyze and understand information. However, if there is a lot of data, it may become challenging for readers to visualize and assimilate information using a pie chart.