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Six Sigma Toolkit: How to Use a Fishbone Diagram

There are many devices and techniques in the Six Sigma practitioner’s toolkit. As Six Sigma professionals, you are expected to use a broad range of skills in your work. One of the most useful devices to have in your repertoire. Fishbone Diagrams are sometimes known as Ishikawa Diagrams, after their founder Dr. Kaoru Ishikawa, and additionally as Cause & Effect Diagrams. When completed, a Fishbone Diagram resembles a fish skeleton (it’s in the name). This is due to the spine- and rib-like structure the diagram forms. Fishbone Diagrams are most useful in group or team-based activities. Moreover, they are used in process improvement to detect root causes that contribute to process issues. This helpful guide will take you through everything you need to know about Fishbone Diagrams, including how to make your own.

Step 1 – Materials For Your Fishbone Diagram

Creating your fishbone diagram will require several materials. In your group, ensure that you have a whiteboard, some butcher block paper, or a flip chart on which to draw. Sticky notes are useful to have on hand when listing potential causes. Sticky notes allow you to re-arrange your notes as you develop your diagram. Cards are a useful alternative. You might want to consider looking into various software packages designed for producing Fishbone Diagrams, such as EngineRoom for Microsoft Excel.

Step 2 – Stating the Problem

Once you have assembled your materials, write down your problem. Try to be as descriptive and detailed as possible. Cover every perspective you can. Write it down on one side of your whiteboard etc. (this side should be labeled Effect, the other Cause) and then draw your backbone. A simple horizontal line pointing towards your problem.

Step 3 – Categorize Your Problem

Next, decide on how you intend to categorize your causes. You can do this either of two ways:

  • By function (the most frequently used approach)
  • Or by process sequence

Now you need to include relevant categories for your diagram, usually manufacturing settings, such as Machine, Process, Resources, Measurement, Staff, Environment, and so on. Policies, or high-level decision rules, sometimes replace tasks like Machine and Process, while Procedures, i.e. particular tasks, replace others. All your categories should branch off of the main backbone to create a fishbone shape.

Step 4 – List Your Causes

Now list all the potential causes. Your diagram will lack detail at this point, but brainstorming sessions with your team will help fill out the remaining categories and subcategories. You can also use whatever data you have available. We find that the 5-Why strategy is a good choice here, as it consistently questions your subject, down to the finest details.

Step 5 – Deep Analysis

We recommend taking your analysis as deep as it will go. Techniques like Regression Analysis and Design of Experiments will help you quantify correlation and causation. Don’t forget, the helpfulness of your diagram depends on how far you develop it. The more detailed your diagram, the more detail with which you have to work. It may take some time, but a rigorous approach to designing your Fishbone Diagram will certainly pay off. As you continue to quantify your variables and contributing causes, add any new information to the chart. Be sure to keep to the fishbone structure, with new causes branching off from parent categories with each new addition. There you have it, your own Fishbone Diagram!

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