How to Create Box Plots

What is a Box Plot

Box Plots or Box and Whisker Plots show statistical values on sums of points with small rectangular boxes, always with the same shape to be easily recognizable.

Here are the symmetrical graphical elements and intervals you’ll see on each symbol:

1. Box – with lower/upper box intervals.
2. Whiskers – with lower/upper intervals, outside the box.
3. Median – small horizontal solid line inside the box.
4. Mean (or Average) – small horizontal dash line inside the box.
5. Outliers – small dots for single extreme data points, outside the box and the whiskers.

You may select different percentage values for both the Box and Whisker intervals.

Steps to Create Box Plots

Start Visual Xtractor or Data Xtractor. Connect to a database. Create or design a SQL query. Run the query and check the results.

1. Display and enable the Chart query builder.
2. Set one or more numeric columns as Point Charts – Box Plot.
3. Adjust the Box and Whisker percentage values.
4. Mix any single-series Box Plot with Scatter and/or Scatter Bar charts.

Box Plot Demo Queries

Look for the ready-to-use Box Plot Chart generated query under the Queries > Demo Queries > Charts > Cartesian Charts folder. Click on the “add demo queries” command link, if not there.

This demo query simply represents as Box Plots three numeric series. We use by default 10% for the upper/lower Whisker intervals, and 25% for the upper/lower Box intervals, but you may select from other predefined values.

The median value is represented with a small solid horizontal line inside the box. The average or mean value is the small dash horizontal line inside a box.

The Box Plot with Scatter Charts demo query renders a single-series Box Plot mixed with related Scatter and Scatter Bar charts, applied on columns with the exact same values.

The four quarter intervals are highlighted on the Scatter chart as well with gray strip bands. Percentage values used for each interval are also displayed as labels.

For current chart, with the default 10% for Whiskers and 25% for Boxes:

• upper and lower Box intervals are between the median line to 75%, and median line to 25%
• upper and lower Whisker intervals are between 75% to 90%, and 25% to 10%
• outliers are dots outside the gray strip band, within the 10% to 0 and 90% to 100% intervals

Customize your Box Plots

1. Change the fixed percentage for both the Box and Whisker intervals.
2. Select another drawing style for the box.
3. Show in 3D.
4. You may also mix single Box Plots with a Scatter and/or Scatter Bar chart.

Conclusion

• Adding Box Plots to a chart in Data Xtractor or Visual Xtractor is fast and intuitive: set one or more numeric data columns as Box Plot, and that’s it.
• Change the fixed percentage numbers for the Whisker and Box intervals.
• Add a Scatter and a Scatter Bar to any single Box Plot chart, on the same values.