Ishikawa (also known as fishbone or cause and effect) diagrams are causal diagrams created in 1968 by Kaoru Ishikaw that depict the causes of a specific event. Each cause or reason that has contributed to a defect is identified as a source of variation or error. The causes are grouped into major categories to help identify them and assist with the creation of preventative or corrective measures. The causal categories include:
- People: Anyone involved with the process
- Methods: How the process is performed, including policies, procedures, or rules
- Machines: Any equipment, computer programs, or tools used to accomplish the task
- Materials: Raw materials, parts, or inputs used to creating the final product
- Measurements: Data collected or generated by the process or data used to evaluate the quality of the product
- Environment: Conditions such as time, temperature, or culture in which the process operates
The causes are typically arrived at during brainstorming sessions with the process owners, whereby they help to label and identify both causes and potential solutions. The use of the five Why techniques can be used to support the identification of root causes.