Box-and-Whisker Plots

Easily compare quality performance and quickly identify opportunities to bring processes in spec—and on target.

What is a Box-and-Whisker Plot?

A box-and-whisker plot is a well-known statistical process control (SPC) comparative analysis tool that can help you eliminate process variation. Use box-and-whisker plots to compare product and process performance, even on different lines or in different plants.

Like a histogram, box-and-whisker plots reveal the distribution of data values. Instead of a histogram’s frequency distribution, box-and-whisker plots represent the distribution with percentiles.

Interpreting Box-and-Whisker Plots

Vertical lines on box-and-whisker plots represent percentiles. The leftmost point on each horizontal line (or “whisker”) represents the minimum value while the rightmost dot represents the maximum value. The line in the center of each box represents the 50th percentile. The box itself spans from the 25th to the 75th percentile. The vertical lines on the whiskers represent the 5th and 95th percentiles.

Compare Against Specification Limits

To extract even more valuable information, box-and-whisker plots can be compared against specification limits. This allows the viewer to understand which data sets are generating the most (and least) out-of-specification issues. As a result, box-and-whisker plots are ideal tools for prioritizing quality activities and Six Sigma projects.

Compare Multiple Process Streams

Box-and-whisker plots are particularly useful for viewing the performance of multiple process streams in the same interface. This capability is useful in any industry that needs to compare performance between production lines, product codes, and shifts.

For example, in food packaging organizations, minimum fill weights are regulated. Underfilling can result in fines or sanctions; overfilling can significantly increase costs.

Box-and-whisker plots quickly reveal vitally important information such as:

Whether products are being filled to minimum required levels
The presence and amount of overfill
Which products run best on which production lines
Which production lines run the same product weights higher (or lower) than others
Whether different shifts fill consistently
Average fill volumes
Variability in fill volumes
Where out-of-specification issues occur the most

Take Another Look at In-spec Data

With the box-and-whisker chart, you can easily discover best practices and opportunities for improvement. Plus, you can examine in-spec data to find savings you might never have expected.

Watch the video to learn more.

What ROI can we expect from SPC software

See the Box-and-Whisker Chart in Action

InfinityQS^® SPC software solutions provide fast and easy access to box-and-whisker charts, without a great amount of time-consuming manual data entry or analysis. See how easy it can be to spot trouble—or opportunities—by surfacing this information from within SPC software.

See how InfinityQS surfaces this information and makes SPC easy.

Modernize and Automate Data Management

Control charts are invaluable for manufacturing optimization. But many manufacturers continue to rely on manual data management methods that are time consuming, frustrating, and vulnerable to inaccuracies.

Learn how you can use affordable real-time SPC software and modern techniques to improve quality management.

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