Fishbone Diagram

Dr Kaoru Ishikawa formulated a visual analysis tool for considering the causes of a specific problem or event. Originally used in the Quality Circle in the 1960s, Ishikawa's diagram offers a systematic way to visualize cause-and-effect relationships and is considered one of the seven basic tools of quality control. The diagrams may be called Ishikawa diagrams, cause-and-effect diagrams or fault trees, but because the diagram itself actually looks like the skeleton of a fish, it is commonly referred to as a fishbone diagram.

The fishbone diagram assists stakeholders in considering a single effect, problem, situation or event and then generating ideas about the causes related to that issue. The process of using the fishbone diagram encourages stakeholders to think through all the possible causes and their relationships to the problem in order to generate an effective solution. Using the fishbone diagram to identify and analyze a specific problem allows stakeholders to organize thoughts about potential causes and arrange the causes by importance. Once the information and ideas have been entered onto the diagram, the visual graphic created illustrates both the relationships and the hierarchy of events.

Using a fishbone diagram may be beneficial to stakeholders who need to answer why or how questions and, furthermore, could be used in a variety of contexts. Historically, the fishbone diagram has been used in quality control and industry, but the potential for using the diagram in other settings is great. Education, community issues, advocacy, environmentalism and other areas where issues arise or changes must be made are also areas where stakeholders would benefit from the careful, systematic and visual analysis of key concerns that using the fishbone diagram allows.

When designing a fishbone diagram, the head of the fish corresponds to the problem, issue, event or objective. Along the spine of the fish skeleton are vertical ribs that summarize the potential causes of whatever has been identified in the head. More detail, subcategories or examples may be added under any category identified as a rib with a horizontal line coming out of the rib. While quality control has typically identified relevant cause categories such as machines, methods, humans, materials and environment, the categories can be modified to suit the analysis needs of the stakeholders. Stakeholders may make up their own categories or may wait to identify categories after themes are recognized in the idea generation phase. It is important to note that when using a fishbone diagram, the problem solvers work backwards. That is, the effect is identified first and the causes of the effect are identified next.

When using a fishbone diagram with a team, the team must first identify a single, key issue to be examined. Once that single issue is identified and written into the head portion of the diagram, group members may brainstorm all possible and real causes of the issue. If the group is using set categories, such as people, places, procedures and policies, or another predetermined set of categories, group members may quickly identify subcategories along the ribs. When [Page 354]the categories have been established, the group must raise questions to determine the contributing factors in each category. Asking the group to answer the question ‘What are the people issues that cause the identified problem?’ establishes the factors to be considered. The group can next consider each factor individually by asking, ‘Why does this happen?’, to determine the subfactors. The process may continue until all potential causes are exhausted, at which point analysis begins.

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