An Ishikawa or fishbone diagram is a visualization tool for categorizing the potential causes of a problem in order to identify its root causes. These diagrams are particularly useful in brainstorming sessions as they help people to focus their conversation.
The technique is named after Dr. Kaoru Ishikawa, a Japanese quality control expert, who invented it to help employees avoid solutions that merely address the symptoms of a much larger problem. The approach begins by stating the problem, and then requires people to identify at least four overall causes or categories that contributed to the problem. Once categories are selected, the team must brainstorm around each cause to further break-down how or why the effect took place.
Because the design of the diagram looks much like a skeleton of a fish, it is commonly referred to as a fishbone diagram.
Common uses of the fishbone diagram range from product design and quality defect prevention to identifying potential factors causing an overall effect or process failure. Each factor or cause for imperfection is a source of variation.
After brainstorming all the possible causes for a problem, users go on to rate the potential causes according to their level of importance and diagram a hierarchy.
Fishbone diagrams are typically worked right to left, with each large “bone” of the fish branching out to include smaller bones containing more detail.
- Create a head, which lists the problem or issue to be studied.
- Create a backbone for the fish (straight line which leads to the head).
- Identify at least four “causes” or categories that contribute to the problem. Major categories often include: equipment or supply factors, environmental factors, rules/policy/procedure factors, and people/staff factors. Connect these four causes with arrows to the spine. These will create the first bones of the fish.
- Brainstorm around each “cause” to document those things that contributed to the cause. Use the 5 Whys or another questioning process such as the 4P’s (Policies, Procedures, People and Plant) to keep the conversation focused.
- Continue breaking down each cause until the root causes have been identified.