Fishbone Diagrams

The fishbone diagram is one of the simplest - and yet powerful approaches to root cause analysis one can find in the traditional 7 Quality Tools package. It is also called Ishikawa Diagram (due to its creator Kaoru Ishikawa) and cause-and-effect diagram. The tool provides the quality practitioner with two powerful features: 1) it is visual and easy to understand, 2) in most cases, it is built during a brainstorming session - which means it involves the people related to the topic being studied. Ishikawa diagrams are qualitative in nature, and should be supported by data and data analysis through the use of other statistical tools. Nevertheless, it offers process improvement teams (PITs) a methodical way of looking into the possible cause(s) related to an outcome. The first step needed to create the diagram is to write down the problem or undesirable result in the "head" of the fish. Then the diagram should be completed by adding "branches" (or bones) that are relevant to the issue being investigated. The figure below suggests six important and commonly used branches.

Materials is the branch related to the physical assets that may be related to the issue or problem statement. Raw materials for example, could be the cause(s) of a poor quality product. Methods refer to the standards and procedures in place that may not be performing well. Machines is the branch that covers the equipment utilized in this particular process - obsolescence as well as wear and tear may be the cause(s) of the the fishbone diagram's problem. Measurements may be related to calibration as well as system and/or machinery metrics that are not delivering accurate readings of the process. Environment can be looked at as both internal environment in which the process performs and the external environment in which either the product itself or the inputs to the process may be contributing to a undesirable outcome. People: is the lack of training, skills, and even motivation causing the process to be a poor one?

Keep in mind that depending on the issue being studied, these headings can be easily adjusted. The most important aspect of a cause-and-effect diagram is to identify the possible cause(s) of a problem. Notice that in the depicted figure above there are sub-branches for each major branch. The quality manager should explore and break down the possible cause(s) as much as possible until the true root cause(s) of the problem has(have) been identified.

As mentioned at the beginning of this post, the Ishikawa diagram is a powerful, easy to understand, and pictorial tool that can be used by any organizational setting, either as a part of a large process improvement study or in a quick meeting that needs to address a small  and specific issue. Give it a try! As usual, our team at eZSigma is available to help in case you need a hand.