Ishikawa diagram
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The Ishikawa diagram (also fishbone diagram or cause and effect diagram) is the brainchild of Kaoru Ishikawa, who pioneered quality management processes in the Kawasaki shipyards, and in the process became one of the founding fathers of modern management. It is simply a diagram that shows the causes of a certain event. It was first used in the 1960s, and is considered one of the seven basic tools of quality management, including the histogram, Pareto chart, check sheet, control chart, flowchart, and scatter diagram. See Quality Management Glossary. It is known as a fishbone diagram because of its shape.
Causes in the diagram are often based around a certain category such as the 6 M's, 8 P's or 4 S's described below. Cause-and-effect diagrams can reveal key relationship among various variables and possible causes provide additional insight into process behaviour.
Causes in a typical diagram are normally arranged into categories, the main ones of which are:
- The 6 M's
- Machine, Method, Materials, Measurement, Man and Mother Nature (Environment) (recommended for manufacturing industry).
- The 8 P's
- Price, Promotion, People, Processes, Place / Plant, Policies, Procedures & Product (or Service) (recommended for administration and service industry).
- The 4 S's
- Surroundings, Suppliers, Systems, Skills (recommended for service industry).
A common use of the Ishikawa diagram is in product design, to identify desirable factors leading to an overall effect. Mazda Motors famously used an Ishikawa diagram in the development of the Miata sports car, where the required result was "Jinba Ittai" or "Horse and Rider as One". The main causes included such aspects as "touch" and "braking" with the lesser causes including highly granular factors such as "50/50 weight distribution" and "able to rest elbow on top of driver's door". Every factor identified in the diagram was included in the final design.
[edit] Appearance
Most Ishikawa diagrams have a box at the right hand side in which is written the effect that is to be examined. The main body of the diagram is a horizontal line from which stem the general causes, represented as "bones". These are drawn towards the left hand side of the paper and are each labeled with the causes to be investigated, often brainstormed beforehand and based on the major causes listed above. Off each of the large bones there may be smaller bones highlighting more specific aspects of a certain cause, and sometimes there may be a third level of bones or more. These can be found using the '5 Whys' technique. When the most probable causes have been identified, they are written in the box along with the original effect. The more populated bones generally outline more influential factors, with the opposite applying to bones with less "branches". Further analysis of the diagram can be achieved with a Pareto chart.
