The fishbone diagram (see below) originally developed by Professor Kaoru Ishikawa, is often referred to as an Ishikawa diagram. The technique can help to structure the process of identifying possible causes of a problem
The diagram encourages the development of an in depth and objective representation ensuring all participants keep on track. It discourages partial or premature solutions, and shows the relative importance and inter-relationships between different parts of a problem.
The method is ideally organized over a number of meetings, enabling the team to become deeply immersed in the problem. Fresh suggestions regarding possible causes can arise during the break and members are more likely to forget who originated every idea, thus making subsequent discussions less inhibited.
The procedure is as follows:
- On a broad sheet of paper, draw a long arrow horizontally across
the middle of the page pointing to the right, and label the arrowhead
with the title of the issue to be explained. This is the ‘backbone’
of the ‘fish’.
- Draw spurs coming off the ‘backbone’ at about 45
degrees, one for every likely cause of the problem that the group
can think of; and label each at its outer end. Add sub-spurs to
represent subsidiary causes. Highlight any causes that appear more
than once – they may be significant.
- The group considers each spur/sub-spur, taking the simplest first,
partly for clarity but also because a good simple explanation may
make more complex explanations unnecessary.
- Ideally, it is eventually re-drawn so that position along the
backbone reflects the relative importance of the different parts
of the problem, with the most important at the head end.
- Circle anything that seems to be a ‘key’ cause, so you can concentrate on it subsequently.
- Kaoru Ishikawa, Guide to Quality Control, Unipub/Quality Resources 1982