A box plot is a diagram of a distribution of data that can highlight up to five key values within that data:
- Minimum value
- 25% quartile
- Median
- 75% quartile
- Maximum value
Box plots are very useful for comparing sets of data - especially the variations in the data. Tableau can plot hundreds of thousands of rows per second, so it can convey much more information than the standard box plot.
Box Plots in Tableau 8.1
Starting with Tableau Desktop 8.1, box plots are available from Show Me and also from a quantitative axis in a view by right-clicking on the axis and choosing Add Reference Line, Band, or Box. If you have Tableau 8.1 see Adding Box Plots in the Tableau Desktop help. If you have an older version of Tableau Desktop, read on to find out how to create a box plot manually.
Creating Box Plots in Earlier Versions of Tableau
Tableau calculates the Median and Quartiles based on the marks that are displayed in the pane. For example, to create a box plot for the profits in each region, you display all the profit values for the region, not the summarized profit value. You can choose to show all the data (to show all the data, on the Analysis menu, cancel the selection of Aggregate Measures), or you can choose a level of detail. This example shows the profits per day in four sales regions.
Step 1
Create a worksheet in Tableau as usual. This example connects to the Sample - Coffee Chain data source.
Step 2
From the Dimensions pane, drag Market to the Columns shelf.
Step 3
From the Measures pane, drag Profit to the Rows shelf.
Step 4
From the Dimensions pane, drag Date to the Marks card, and drop it on the Level of Detail shelf.
Step 5
Right-click the Date field and select All Values.
Step 6
At the top of the Marks card, click the list and select Line.
Step 7
From the Dimensions pane, drag Date to the Marks card, and drop it on the Path shelf.
Step 8
On the Path shelf, right-click the Date field and select All Values.
Step 9
Right-click to the left of the vertical axis and select Add Reference Line.
Step 10
In the Add Reference Line dialog box, select the Distribution pane.
Step 11
Under Scope, select Per Cell.
Step 12
Under Computation, click the Value list, and select Quantiles. Be sure to keep Number of Tiles set to 4.
Step 13
In the Label list, select None.
Step 14
Under Formatting, click the Line list, then select the solid line. For this example, select the second thickness from the left, and the bright red color square (second down the third column from the left).
Step 15
Under Formatting, select Symmetric.
Step 16
Click the Fill list, and for this example, select the charcoal gray square (second down in the leftmost column).
Step 17
When finished, click OK.
The view now shows box plots.
Step 18
To add a line for the maximum profit to the box plot, repeat steps 9 through 17 (skipping steps 15 and 16), but this time:
- In Step 10, select the Line pane instead of the Distribution pane.
- In Step 11, instead of Quantiles, select Maximum.
Step 19
To add a line for the minimum profit to the box plot, repeat steps 9 through 17 (skipping steps 15 and 16), but this time:
- In Step 10, select the Line pane instead of the Distribution pane.
- In Step 11, instead of Quantiles, select Minimum.
