A cause and effect diagram is a visualisation tool used to categorise the potential causes of a problem. This tool is used to identify the root causes of a problem, as we saw in our article of 7 October 2022. Generally used for root cause analysis, the fishbone diagram combines the practice of brainstorming with a mind-mapping model. It should serve as an effective testing technique for determining causes and effects.
Also known as a fishbone diagram, it is useful in product development and troubleshooting processes. It is generally used to focus a conversation around a problem. After the group has brainstormed all the possible causes of a problem, the facilitator helps the group rank the potential causes according to their level of importance and establish a hierarchy. The diagram takes its name from its shape, which resembles the skeleton of a fish. Fishbone diagrams are generally developed from right to left, with each major “bone” of the fish branching out to include smaller bones, each containing more detail.
Kaoru Ishikawa, a Japanese quality control expert, invented the cause and effect diagram to help employees avoid solutions that merely treat the symptoms of a much larger problem. Cause and effect diagrams are considered one of the seven basic quality tools and are used in the “analyse” phase of the Six Sigma DMAIC approach (define, measure, analyse, improve, control) to solve problems.
How to create a cause and effect diagram
Cause and effect diagrams are generally produced during a team meeting and drawn on a flip chart or whiteboard. Once a problem requiring further investigation has been identified, teams can follow the steps below to create the diagram:
The head of the fish is created by listing the problem as a statement and drawing a box around it. A horizontal arrow is then drawn across the page, pointing towards the head. This is the backbone of the fish.
Next, at least four primary "causes" that could contribute to the problem are identified. Generic starting categories include methods, skills, equipment, people, materials, environment or measurements. These causes are then drawn branching off the backbone with arrows, forming the first bones of the fish.
For each main cause, team members should brainstorm any additional information that may contribute to it. This generally involves questioning methods such as the 5 Whys or the 4Ps (Policies, Procedures, People and Plant) to keep the conversation focused. These contributing factors are noted down so that the corresponding cause can be derived from them.
This process of breaking down each cause is continued until the root causes of the problem have been identified. The team then analyses the diagram until an outcome and next steps are agreed.
When to use a cause and effect diagram
Here are some reasons why a team might consider using a fishbone diagram:
- To identify the possible causes of a problem.
- To help develop a product that addresses the shortcomings of current market offerings.
- To reveal bottlenecks or weak points in a business process.
- To prevent recurring problems or employee burnout.
- To ensure that any corrective action put in place will solve the problem.
Xavier Schuster
Consultant at SXE Consulting. Industrial consulting firm based in Luxembourg, 25 years of experience in operational excellence.
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