Ishikawa diagrams (also called fishbone diagrams or cause-and-effect diagrams) are diagrams that show the causes of a certain event. Common uses of the Ishikawa diagram are to identify potential factors causing an overall effect. Each cause or reason for imperfection is a source of variation. Causes are usually grouped into major categories to identify these sources of variation.
Ishikawa diagrams were proposed by Kaoru Ishikawa in the 1960s, who pioneered quality management processes in the Kawasaki shipyards, and in the process became one of the founding fathers of modern management.
It was first used in the 1960s, and is considered one of the seven basic tools of quality management, along with the histogram, Pareto chart, check sheet, control chart, flowchart, and scatter diagram. It is known as a fishbone diagram because of its shape, similar to the side view of a fish skeleton.
How is this Relevant to ProcessModel, Process Improvement and Simulation?
- In some processes you will find problems for which the cause cannot be easily determined.
- ProcessModel has a great “fishbone” diagramming tool built-in
When To Use It
You may find it helpful to use the Ishikawa diagram in the following cases:
- To analyze and find the root cause of a complicated problem
- When there are many possible causes for a problem
- If the traditional way of approaching the problem (trial and error, trying all possible causes, and so on) is very time consuming
- The problem is very complicated and the project team cannot identify the root cause
Then Not To Use It
Of course, the Fishbone diagram isn’t applicable to every situation. Here are a just a few cases in which you should not use the Ishikawa diagram because the diagrams either are not relevant or do not produce the expected results:
- The problem is simple or is already known.
- The team size is too small for brainstorming.
- There is a communication problem among the team members.
- There is a time constraint; all or sufficient headcount is not available for brainstorming.
- The team has experts who can fix any problem without much difficulty.
Causes in the diagram are often categorized, such as to the 4 M’s, 8 P’s or 4 S’s described below. Cause-and-effect diagrams can reveal key relationships among various variables, and the possible causes provide additional insight into process behavior.
Causes can be derived from brainstorming sessions. These groups can then be labeled as categories of the fishbone. They will typically be one of the traditional categories mentioned above but may be something unique to the application in a specific case. Causes can be traced back to root causes with the 5 Whys technique. Typical categories are:
The 4 M’s (Used in manufacturing)
- Machine (Equipment)
- Method (Process/Inspection)
- Material (Raw,Consumables etc.)
- Man power
The 8 P’s (Used in service industry)
- Physical Evidence
- Productivity & Quality
The 4 S’s (Used in service industry)
- Define the problem
- Identify the causes
- Elliminate unimportant causes
- Take action on remaining causes
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