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Also Called: Cause–and–Effect Diagram, Ishikawa Diagram
Variations: cause enumeration diagram, process fishbone, time–delay fishbone, CEDAC (cause–and–effect diagram with the addition of cards), desired–result fishbone, reverse fishbone diagram
The fishbone diagram identifies many possible causes for an effect or problem. It can be used to structure a brainstorming session. It immediately sorts ideas into useful categories.
Materials needed: flipchart or whiteboard, marking pens.
This fishbone diagram was drawn by a manufacturing team to try to understand the source of periodic iron contamination. The team used the six generic headings to prompt ideas. Layers of branches show thorough thinking about the causes of the problem.
Fishbone Diagram Example
For example, under the heading “Machines,” the idea “materials of construction” shows four kinds of equipment and then several specific machine numbers.
Note that some ideas appear in two different places. “Calibration” shows up under “Methods” as a factor in the analytical procedure, and also under “Measurement” as a cause of lab error. “Iron tools” can be considered a “Methods” problem when taking samples or a “Manpower” problem with maintenance personnel.
Excerpted from Nancy R. Tague’s The Quality Toolbox, Second Edition, ASQ Quality Press, 2005, pages 247–249.
Analyze process dispersion with this simple, visual tool. The resulting diagram illustrates the main causes and subcauses leading to an effect (symptom). Start using the Fishbone tool (Excel, 39 KB).