The Fishbone diagram, also known as the Cause-and-Effect diagram or Ishikawa diagram is a tool to identify and present all the possible causes of a particular problem grouped into categories, in a systematic and graphical format. The diagram represents the bone structure of a fish. A box at the head contains the statement of the problem. The spine or the main line has different branches for different categories of problems, and each branch has different boxes, to list specific issues or problem. Each box can branch outward, and with each branch, the level of detail increase, and the outermost branch usually identifies the root cause of the problem.
Although there is no hard and fast rule regarding the number or nature of branches, many manufacturing related fishbone diagrams use five branches for 'Man', 'Machine', 'Materials', 'Methods, and 'Measurement', while others use 8 P's, for “Procedures," “People," “Price," “Promotion," “Processes," “Plant," “Product," and “Policies." Or the 4 S's of “Skills," “Surroundings," “Systems," and “Suppliers."