Cause and Effect diagrams have been illustrated in many ways. One of the most novel is called the "fishbone" or "Ishikawa" diagram, named after Dr. Kaoru Ishikawa, it's originator. Dr. Ishikawa was an expert in Quality Control Theory. Why it is called "fishbone" becomes obvious when the diagram is completed, in that it looks like a fish skeleton.



The analysis starts with a problem to be investigated. This problem is written in the form of a question on the right side of the page. An arrow, or sometimes a drawing of a fish head, will point to the question under consideration. To the left of the problem statement, a horizontal line divides the paper in two. This is the "backbone" of the fishbone diagram.

The following group of bones symbolize main categories of facts that might be a part of the main cause. These category titles are inscribed on the paper at the top and the bottom. Arrows placed on an angle are arranged in a backwards and forwards pattern, that make a herringbone pattern.

Conventions have developed to provide starting categories appropriate for different types of problems domains. In manufacturing, the 6 M's are used: Machine, Methods, Materials, Maintenance, Man, and Mother Nature. Modern analysis of manufacturing problems adds categories like: Equipment, Process, People, Materials, Environment, and Management. The 8 P's are a useful starting point for analysis of service and administrative problems: Price, Promotion, People, Processes, Place / Plant, Policies, Procedures, and Product. A service industry may also use the 4 S's: Surroundings, Suppliers, Systems, and Skills.

Analysis gets underway after the fundamental skeletal structure is in position. Variables are listed that play a part in each subset of elements that result in the underlying or root cause. These are displayed on top of arrows directing you to the subset lines, which themselves may possess lines of their own directing toward them, further delineating the variables that play a part. While this may proceed ad infinitum, naturally it will be hard to sketch more than a minimal number of levels.

As the skeleton of the diagram comes together, the team begins to brainstorm and look for solutions to the outlined problem. It is often helpful that the problems be phrased in the form of a question, such as, "Why is this happening?" and "What issues are contributing to this complication?" Team members can be asked to answer these questions in the context of each category of problems.

Team members think of useful items to add to the diagram. When they run out of ideas, the brainstorming stops. Then the results are studied in order to find the likeliest cause of the problem. If the same issue appears in multiple categories, it if fair to assume that this is an important root cause. Areas of the diagram are also studied as these areas may also point to something significant.