The fishbone diagram (also known as the Ishikawa or cause-and-effect diagram) is a common tool to identify or prevent a particular event. The diagram was popularized in the 1960’s in the Kawasaki shipyards by Kaoru Ishikawa, who would become a founding father of modern management. It gets its name due to the resemblance of a fish skeleton, with the effect at the fish’s head and the grouped causes extending out like fish bones. The Ishikawa diagram is a cause analysis tool (along with the 5 Whys, Pareto chart, or Scatter diagram) used during root cause analysis to group causes into different sub-categories that are used as the “bones” of the diagram (measurements, materials, methods, etc.). Used effectively, the diagram helps teams brainstorm and categories all potential causes for a failure rather than focus only on the symptoms.
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When to Use Ishikawa Diagram
The Ishikawa diagram is a versatile tool that can be used in almost any system or process to break down varying causes. During a root cause analysis, the diagram should be used during the analysis phase to categorize contributing factors.
The tool can also be used:
- To dissect a problem statement
- To improve a process or system
- To evaluate a new design
Fishbone diagrams are used during a root cause analysis as a way visualize the relationship between variable causes and a particular problem. Below is the general procedure when using the fishbone diagram:
- Determine the problem or effect and place it to the far right of the graph (the fish’s head)
- Categorize the major causes of the effect and use these as the headings for each fishbone
- Brainstorm all causes for the effect and group these horizontally along the main causal categories
- Determine sub-causes by using the 5 Whys technique (also including environment)
Advantage and disadvantages
While the Ishikawa diagram is an important tool to identify the underlining root causes of a effect, like all tools, it comes with its own advantages and disadvantages.
- Ishikawa diagram is a visual brainstorming tool that’s helpful for visualizing issues to stakeholders
- By visually brainstorming various causes, the diagram prevents teams from limiting their scope or thinking
- Repeatedly asking “why” at various stages drills down the root cause
- Displays multiple causes simultaneously and gives high-level view
- Effects that are the result from multiple causes the diagram to become overly complex and unwieldy
- The interrelationship between causes are not readily apparent
- Not all listed causes have a direct impact on the effect being studied. It can be difficult to differentiate relevant and non-relevant causes which leads itself to low success rates as teams do not have the time or resources to address every possible cause
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