A fishbone diagram, also called a cause and effect diagram or Ishikawa diagram, is a visualization tool for categorizing the potential causes of a problem in order to identify its root causes.
Dr. Kaoru Ishikawa, a Japanese quality control expert, is credited with inventing the fishbone diagram to help employees avoid solutions that merely address the symptoms of a much larger problem.
A fishbone diagram is useful in brainstorming sessions to focus conversation. After the group has brainstormed all the possible causes for a problem, the facilitator helps the group to rate the potential causes according to their level of importance and diagram a hierarchy. The design of the diagram looks much like a skeleton of a fish. Fishbone diagrams are typically worked right to left, with each large "bone" of the fish branching out to include smaller bones containing more detail.
Fishbone diagrams are used in the "analyze" phase of SixSigma's DMAIC (define, measure, analyze, improve, control) approach to problem solving.
How to create a fish diagram:
- 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” that contribute to the problem. 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.
This example illustrates how a group might begin a fish diagram to identify all the possible
reasons a web site went down in order to discover the root cause.