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.
  • Shaped somewhat like a fish, these charts are sometimes called 'Fishikawa' diagrams.
  • Ishikawa diagrams follow a series of eight steps to construct.

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.

Process to Make an Ishikawa Diagram

To make an Ishikawa Diagram, a group will need a white board, 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 to areas in the chart where ideas are thin.