What is the name of the diagram that is often used to show the different layers of the system?

What Is an Ishikawa Diagram?

An Ishikawa diagram is a diagram that shows the causes of an event and is often used in manufacturing and product development to outline the different steps in a process, demonstrate where quality control issues might arise, and determine which resources are required at specific times.

The Ishikawa diagram was developed by Kaoru Ishikawa during the 1960s as a way of measuring quality control processes in the shipbuilding industry.

Key Takeaways

• An Ishikawa diagram is used to show the causal factors that go into some final outcome, often related to a production or design problem.
• They are named after Japanese engineering professor Kaoru Ishikawa in the 1960s, who helped apply them to manufacturing processes.
• Shaped somewhat like a fish, these charts are sometimes called fishbone or 'Fishikawa' diagrams.
• Ishikawa diagrams often follow the "Six M's": manpower, machinery, methods, materials, measurement, and mother nature.

Understanding Ishikawa Diagrams

Ishikawa diagrams are sometimes referred to as fish bone diagrams, herringbone diagrams, cause-and-effect diagrams, or Fishikawa. They are causal diagrams created by Kaoru Ishikawa to show the causes of a specific event. They resemble a fish skeleton, with the "ribs" representing the causes of an event and the final outcome appearing at the head of the skeleton. The purpose of the Ishikawa diagram is to allow management to determine which issues have to be addressed in order to gain or avoid a particular event.

Other common uses of the Ishikawa diagram include using it as a methodology for creating product designs that solve practical problems. It can also be used in quality defect prevention 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 and classify these sources of variation.

How to Make an Ishikawa Diagram

To make an Ishikawa Diagram by hand, a group will need specialized software or else a whiteboard, flip chart, and some marking pens.

1. The group should agree on a problem statement (effect).
2. Write the problem statement at the center-right of the flipchart or whiteboard, box it, and draw a horizontal arrow running to it.
3. Brainstorm the primary categories of causes for the problem. For instance, it might make sense to start with these generic headings: methods, machines (equipment), people (manpower), materials, measurement, and environment.
4. Write the categories of causes as branches from the main arrow.
5. Brainstorm possible causes. Ask: “Why does this happen?” As each idea is given, the facilitator writes it as a branch from the appropriate category. Causes can be written in several places, if they relate to several categories.
6. Ask the question “why does this happen?” again. Write sub–causes branching off the causes. Continue to ask “Why?” and generate deeper levels of causes. Layers of branches indicate causal relationships.
7. When the group runs out of ideas, focus attention on areas in the chart where ideas are thin.

The 6 Ms of an Ishikawa Diagram

Each of the "bones" or "ribs" in a classic Ishikawa diagram represents an issue relevant to quality control, and may be described by the six "M"s, where failures or potential failures can be identified and rectified. These are:

• Manpower - the training, skill, and attitude of the employees or workers
• Machines - maintenance of machines, whether upgrades to better technology is needed
• Materials - are raw materials and inputs properly labeled, stored, and of high quality. Have they been ordered in the right size and quantity
• Measurement - are methods of measurement and control correct and accurate, do they need to be adjusted
• Mother Nature - often uncontrollable environmental factors like fire or bad weather, but certain safety measures can be undertaken, as well as insurance purchased for damage or disaster
• Method - does the production process have the most efficient number of steps, are there bottlenecks, is it overly complex and error-prone

Advantages and Disadvantages of an Ishikawa Diagram

Ishikawa diagrams are intuitive and easy to understand at a glance. By splitting a business's operations into different segments (e.g. machines, manpower, etc.), the root cause of problems can be better identified and addressed. It also has a flexible structure where various "ribs" can be amended, removed, or replaced as necessary in order to coincide with a particular business or organization.

Its simplicity, however, can also be its biggest drawback as it does not necessarily reveal the size or importance of any one issue, making it more difficult to prioritize action. This means that small problems may be given more attention than they need and large ones not enough. Because much of the diagram's inputs and interpretations are subjective, it can also lead to disagreements among managers who view the chart from different perspectives.

Pros and Cons of Ishikawa Diagrams

Pros

• Easy to construct

• Flexible and generic

• Helps find the root cause of problems

Cons

• Can be oversimplified

• Does not prioritize problems by importance

• Subjective

What Is an Ishikawa Diagram Used For?

Ishikawa diagrams are management tools used for quality control that help identify the root causes of problems or defects found in business operations.

Why Is it Called an Ishikawa Diagram?

Also known as a fishbone diagram, the name Ishikawa is derived from the Japanese academic Kaoru Ishikawa, who in the 1960s, popularized its use in Japanese industry.

What Are the Categories Included in a Fishbone Diagram?

While any number of categories may be used to fit a particular business, most often a fishbone diagram appears with six: manpower, materials, methods, machines, measurement, and environment (mother nature). These comprise the six M's of an Ishikawa Diagram.

The Bottom Line

Ishikawa diagrams are schematic drawings that identify possible root causes for production defects or concerns. Each cause context (e.g., manpower, machinery, methods, materials, measurement, mother nature/environment) is drawn as if the ribs on the skeleton of a fish, giving the charts the alternative name fishbone diagram. By allowing managers to quickly narrow down the root cause(s) for various issues, they can be quickly addressed, However, the relative magnitude or importance of an issue is left unknown in an Ishikawa diagram, and its interpretation open to subjectivity.

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