A Worksheet for Ishikawa Diagrams

A Perkin tracker combines the benefits of brainstorming with an action-item tracking list

Published: Wednesday, March 30, 2016 - 14:55

The start of a failure investigation may involve brainstorming, but empirical methods will be required to actually identify a problem's cause. Implementing an improvement action without a confirmed root cause risks a reoccurrence of the issue because the true root cause has yet to be addressed.

The Ishikawa diagram, a cause-and-effect diagram created by Kaoru Ishikawa, is a common and useful tool for investigating failures and can be effective in facilitating brainstorming sessions. However, it may not be specific enough for a root-cause analysis team to identify evaluation methods for the hypothesized causes listed in the Ishikawa diagram (aka fishbone diagram). Additionally, once completed, the diagram contains great information, but isn't very useable or actionable by itself.

Fortunately, this weakness can be addressed easily by using a simple spreadsheet to translate brainstormed ideas into actionable hypotheses. I call such a spreadsheet a "Perkin tracker," named after the person who introduced me to the concept. Such a spreadsheet can be used to turn concepts in an Ishikawa diagram into hypotheses that can then be evaluated empirically.

Figure 1 depicts a typical Ishikawa diagram with the six branches labeled as material, method, milieu (environment), man (employee), measurement, and machine. Various potential root causes would then be listed under each branch.

Figure 1: Ishikawa diagram

Figure 2 shows a close-up of the "material" and "machine" branches of the diagram. Each branch has two items; however, it might not be clear what actions should be taken to investigate these hypotheses. The reasons these items could cause the failure may also be unclear from just glancing at the Ishikawa diagram.

Figure 2: Ishikawa diagram for a crack in a part

The items in the Ishikawa diagram can be copied to a Perkin tracker spreadsheet such as the one shown in figure 3. This combines the benefits of the brainstorming from an Ishikawa diagram with an overview provided by a more traditional action-item tracking list. In a Perkin tracker, the actions to take can be described. If necessary, the content of each branch and "twig" can then be updated with guidance as to how the item could have caused the failure. For example, wrong material used on the material branch could receive the note: "Incorrect material was not sufficient for the usage."

Figure 3: Perkin tracker spreadsheet. Click here for larger image.
Click here for blank worksheet in Excel

The Perkin tracker has three levels of prioritization to decide which hypotheses should be evaluated first. In an ideal world, all hypotheses would be immediately tested, but resources may be limited, so those believed to be highly linked to the problem should be tested first. Hypotheses with a weaker connection to the problem may also have a high priority for evaluation if testing them is quick, easy, and inexpensive.

The spreadsheet should be used as an action plan. Each evaluation is assigned a person responsible for performing it, along with a deadline. After completion, the results should be listed in the Perkin tracker and then evaluated for their link to the root cause of the problem. Items linked to the cause should be verified, and any other items identified as potentially linked to the problem should be investigated further.

Transferring the Ishikawa diagram to a spreadsheet makes the diagram, an already powerful root cause analysis tool, even more useful by providing testable hypotheses as well as a tracking list for managing the root-cause investigation. With such a worksheet, the team can easily track the status of action items and see a brief summary of the results. This makes a more complicated issue much easier to manage.

About The Author

Matthew Barsalou

Matthew Barsalou is a statistical problem resolution master black belt at BorgWarner Turbo Systems Engineering GmbH. He is an ASQ-certified Six Sigma Black Belt, quality engineer, and quality technician; a TÜV-certified quality manager, quality management representative, and quality auditor; and a Smarter Solutions-certified lean Six Sigma Master Black Belt. He has a bachelor’s degree in industrial sciences, and master’s degrees in engineering, business administration, and liberal studies with emphasis in international business. Barsalou is author of Root Cause Analysis, Statistics for Six Sigma Black Belts, The ASQ Pocket Guide to Statistics for Six Sigma Black Belts, and The Quality Improvement Field Guide.