A fishbone diagram, also known as a cause and effect diagram or an Ishikawa diagram, is a visual tool for identifying, categorizing, and illustrating the potential causes of a specific problem or effect. The name “fishbone” comes from the shape of the diagram, which resembles the skeleton of a fish.
The diagram was popularized by Kaoru Ishikawa in the 1960s, a Japanese quality control statistician who introduced this method as a systematic tool to discover and present all possible causes of a particular problem in a structured format.
The structure of the diagram includes:
- Head: The head of the fishbone represents the problem or effect. It’s usually stated in the form of a question.
- Spine: The long, horizontal arrow running across the diagram is called the spine. This links the head to the bones.
- Bones: The bones along the spine represent the main categories of potential causes. Common categories used in manufacturing industries include “People,” “Methods,” “Machines,” “Materials,” “Measurement,” and “Environment,” often referred to as the 6Ms. However, these categories can be customized to suit the specific problem and the context of the situation.
- Sub-bones: Branching off each bone are sub-bones or smaller bones. These represent more specific causes related to the main category. Sub-bones can further branch out as needed.
A fishbone diagram is especially useful in a brainstorming session to identify potential causes of a problem. It helps teams categorize and visualize possible root causes, promoting systematic problem-solving and a clear understanding of the factors contributing to a problem. The ultimate goal is to pinpoint where changes can be made to solve or prevent the problem effectively.
Example of a Fishbone Diagram
Let’s consider a hypothetical problem in a manufacturing plant: “Product defects are increasing.” The aim is to use a fishbone diagram to identify and categorize potential causes of this problem.
Here’s how the diagram might be structured:
Head (Problem/Effect): Increased product defects
Spine: Central, horizontal arrow connecting the problem to the potential causes.
Bones (Major Cause Categories):
- People: This could refer to insufficient training, lack of experience, or fatigue affecting the workers on the production line.
- Methods: This could encompass inefficient production processes, outdated quality control measures, or non-adherence to procedures.
- Machines: This category might include faulty equipment, improper machine maintenance, or outdated technology.
- Materials: This could involve poor quality of materials, unreliable material suppliers, or improper storage and handling of materials.
- Measurement: This might include inaccurate testing equipment, lack of quality measurement checks, or faulty data analysis.
- Environment: This could refer to poor working conditions, such as excessive heat, cold, or noise, and other environmental factors that might affect the production process.
Each of these main “bones” could then have “sub-bones” branching off, representing more specific causes. For instance, under “People,” you might have sub-bones like “insufficient training on machine X,” “shifts too long leading to fatigue,” etc.
By fleshing out this diagram in a team setting, the manufacturing plant can get a clear visualization of all possible root causes for the increase in product defects. The team can then investigate these potential causes further, validate them, and ultimately determine which are contributing to the problem, providing a roadmap for corrective action.