Box Plot

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Box Plot

The "box" part of a box plot shows the locations of the 25th, 50th, and 75th percentiles. The box plot's "whiskers" extend out to the end of the range. Box plots are particularly useful for comparing attribute values for several different groups.

The example shows how much students' backpacks weigh as a percentage of their body weight. These results are shown separately for students in grades one, three, five, and seven. The box plots show that the older students tend to carry backpacks that are a higher percentage of their body weight. They also show that there is more variability (spread) in how much students carry at the higher grades than at the lower grades.

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To make a box plot,

1.	Put a numeric attribute on the horizontal axis. From the data cards, drag the name of a numeric attribute onto the horizontal axis of the plot (the lower part of the plot will highlight to indicate when you can drop).

2.	Fully separate the attribute. In the plot, drag any case icon all the way to the right (until there are no bin lines). This will fully separate that attribute horizontally.

3.	Add a box plot display. In the upper plot toolbar, click the small triangle to the right of the Hats button and choose Box Plot from the menu.

In the example, the icons were stacked horizontally (click the Stack Horizontal button in the upper plot toolbar), case icons were made very small (adjust the slider in the lower plot toolbar), and another attribute (Grade) was added to the vertical axis (drag the attribute name from the data cards to the left side of the plot). As an option, you can set the box plots to show outliers (choose Show Outliers from the Hat Options menu).

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