In root cause analysis, the Fishbone diagram can be used to facilitate root cause analysis for a specific problem. The fishbone diagram provides a structured method for identifying and documenting potential root causes during the brainstorming process, encouraging teams to think about a problem in a systematic fashion, digging deeper to discover less obvious root causes.
The fishbone diagram is also known as a cause and effect diagram. In some circles, it is referred to as an Ishikawa diagram, after its innovator, Dr. Kaoru Ishikawa, the Japanese quality control expert. The popular name for this chart, however, "fishbone", stems from the fact that the diagram resembles the skeleton of a fish.
The Fishbone Analysis process
Fishbone analysis starts with a problem to be investigated. This problem is written in the form of a question on the right side of the page. An arrow, or sometimes a drawing of a fish head, will point to the question under consideration. To the left of the problem statement, a horizontal line divides the paper in two. This is the "backbone" of the fishbone diagram. The next set of bones represent major categories of factors that could contribute to the root cause. These category names are written along the top and the bottom of the paper. Angled arrows point back to the backbone and toward the head, forming a herringbone pattern. Conventions have developed to provide starting categories appropriate for different types of problems domains.
- In manufacturing, the 6 M's are used:
- Machine,
- Methods,
- Materials,
- Maintenance,
- Man, and
- Mother Nature.
- Modern analysis of manufacturing problems adds categories like:
- Equipment,
- Process,
- People,
- Materials,
- Environment, and
- Management.
- The 8 P's are a useful starting point for analysis of service and administrative problems:
- Price,
- Promotion,
- People,
- Processes,
- Place / Plant,
- Policies,
- Procedures, and
- Product.
- A service industry business may also use the 4 S's:
- Surroundings,
- Suppliers,
- Systems, and
- Skills
Once the basic skeletal frame is in place, the fishbone analysis begins by listing factors that contribute to each category of issues that produce the root cause. These are written above arrows that point back to the category line. These lines in turn can have their own lines pointing into them, breaking down factors that contribute to it. This can go on infinitely, but will be difficult to draw beyond a few levels for obvious reasons.
With the skeleton of the fishbone diagram in place a team brainstorms about each category, looking for reasons that produce the end result. Generally, it is good to phrase a problem as a question and ask team members to answer the question in the context of each category. In general, the question is "Why is this happening?" Then, for each category, the question shifts to "How are factors in this category causing this?"
The brainstorming continues until team members can no longer think of useful items to add to the diagram. At this point, the results are analyzed to identify the most likely root causes of the problem. Finding the same issue within multiple categories is a good indication that it is an important root cause in the system. Likewise, areas of the diagram that are densely populated with detail are likely to point to areas of significance.
Daiv Russell is a management consultant with Envision Consulting in Tampa, Florida. Learn more about Fishbone Analysis - Using Ishikawa's Fishbone Diagram for Root Cause analysis.
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