Ishikawa Diagram

Ishikawa Diagram

Investopedia / Mira Norian

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.

Ishikawa Diagram
Image by Julie Bang © Investopedia 2020

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.

Types of Ishikawa Diagrams

At its core, Ishikawa diagrams are the same. However, there are different types that rely on different categories that may spur different innovative or strategic thinking. Here are the more common types of Ishikawa diagrams.

The 6 M's 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?

The 3 M's Ishikawa Diagram

A simple variation to the 6 M's Ishikawa diagram is the 3 M's diagram. In this variation, only "man", "machine", and "materials" are used. This may be more commonly seen in manufacturing processes that may experience less interaction with mother nature or processes that do not need constant measuring or refinement.

The 8 P's Ishikawa Diagram

Similar to the classic 6P diagram, a variation organizations information into eight different categories listed below.

  • Procedures - What are the set of instructions in place to complete a task or activity?
  • Policies - What internal rules dictate how things are done, and are they being followed accordingly?
  • Place - Where are events occurring, are there better locations the events could occur, and what are the implications of events happening at these places?
  • Product - What is being produced, why is it being produced, and what else could be produced?
  • People - Who is involved in the process, and who is incorrectly being omitted from processes?
  • Processes - What are the steps of a process, and are they being followed accordingly?
  • Price - What are the financial inputs of the process, and what are the financial outputs of the process?
  • Promotion - How are goods introduced to the market, and what strategies are used to convey the benefits of the product?

The 4 S's Ishikawa Diagram

The 4S Ishikawa diagram has less bones or ribs, as it only breaks categories into four components. This diagram is more suited for the service industry as it omits categories that would be more helpful when contemplating a product or manufacturing process.

  • Suppliers - Who do we rely on for goods, and what do we need from these third-parties?
  • Systems - What overarching processes are in place, and how can they be improved or changed to better serve a customer?
  • Surroundings - What physical experience does a customer have when they engage with our business, and what circumstances in close proximity to our business impact the way we operate?
  • Skills - What talents do we have, what talents do we need, and what do customers demand from us that we must be good at?

A simple fishbone diagram does not have any predetermined categories. Instead, the organization sets forth the categories it things are most useful to analyze. They may be parts of each diagram mentioned above or entirely different categories.

When to Use an Ishikawa Diagram

An Ishikawa diagram has several uses and can visualize potential causes of problems in many different circumstances. These diagrams are helpful for product developers when new items are being created. This also helps teams identify which resources will be needed at specific times to identify quality control issues before they occur.

Ishikawa diagrams also aid more established products by troubleshooting processes. When a problem arises and management can not find the cause, they may use Ishikawa diagrams to break the problem into smaller pieces until the root issue is found and resolved.

Ishikawa diagrams are more useful when there is a known problem that a company can identify. The company must also be able to observe the problem, as this information will ultimately be fed into the diagram. The diagram may be used to depict management's hypothesis on what happened and explain how the problem may be resolved.

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

  • Easy to construct

  • Flexible and generic

  • Helps find the root cause of problems

  • 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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