Project Management Games, Six Sigma, Business Word Games and Puzzles

Fishbone Diagram for Root Cause Analysis
Also known as Ishikawa diagram
Contributing Editor

The Fishbone Diagram (or, cause-and-effect diagram), also known as Ishikawa diagram, shows the causes and effect relationship of a certain event. A common industrial use of the Ishikawa diagram is in product design, where it is effective in identifying systemic factors contributing to an overall environmental effect.

Origins
The fishbone diagram (so called because of its similarity to a fish skeleton), is properly known as Ishikawa diagram; named after Kaoru Ishikawa who in the 1960s pioneered quality management processes in the shipyards of Kawasaki. Ishikawa became famous for his studies and later was regarded as one of the founding fathers of modern quality management processes.

This quality management concept, initially applied during the '60s, is still today considered among the seven fundamental tools of quality management, which includes the Pareto chart, check sheet, histogram, scatter diagram, control chart, and flowchart. Please refer to our Six Sigma Glossary on this website for more information.

Classic Ishikawa
The classic Ishikawa diagram includes a vertical line. To the right of the line is a box in which the overall effect (or problem) from the process, is noted. The main body of the fishbone diagram includes a horizontal line to the left of the vertical line. The systemic "cause lines" are attached to the horizontal line, similar to the "bones" of the fish, inclined towards the back-left of the diagram. The "cause lines" each have a box attached with the causes to be investigated. It is recommended that the problem be brainstormed beforehand and the resulting diagram should include the major causes from a list of possible causes.

After proper due diligence and brainstorming the the most probable causes for problem in the process should have been detected. They are then noted in the box attached to the "Cause lines". Notice that from each of the large fish bones (cause lines) there are smaller bones indicating more finite reasons for certain causes. It is possible to have a hierarchy of additional smaller bones indicating further causes.

Heuristic
As a rule of thumb, the bones with more finite lines usually indicate the existence of more influential factors. The opposite is true for the "cause lines" fishbones with fewer finite bones. Discovery of these deep causes are often facilitated by employing the "5 Whys" technique. Further cause and effect analysis of the process can be carried out using a Pareto chart.

Take Action
Once all these underlying causes are discovered and documented, the project team can implement corrective actions, and establish tools to monitor and control the process in order to maintain it within performance specifications.

Six Sigma - Ishikawa Root Cause Analysis