What type of diagram also called a fishbone or Ishikawa diagram helps find the root cause of a quality program?

What is a Fishbone (Ishikawa) Diagram?

The Fishbone Diagram, also known as the Ishikawa Diagram, is a visual technique for problem-solving invented by Kaoru Ishikawa, a Japanese quality control expert. In manufacturing, the Fishbone Diagram is an effective technique for causal analysis. It aids people in identifying potential causes of a problem and is an especially helpful brainstorming tool when problem-solving is blocked and little quantitative data is available.

How does a Fishbone Diagram work?

The Fishbone Diagram is usually read from left to right and consists of bones, indicating possible causes of a problem, connected to a spine leading into the fish’s head, which symbolizes the defect or problem.

For example, in the diagram below, the shape of a fish’s skeleton is formed by possible causes, grouped by category, for a failed inspection. Here, the causes are categorized by the “5 M’s” in manufacturing: machine, method, material, man/mind power, and measurement/medium. Using these as prompts to generate hypotheses for the root cause of a problem, you write the potential causes under each of these on the “ribs” of the fish. In the image below, for example, the problem is that 12% of the product fails inspection, and one of the potential causes of this related to the materials is that screws were worn.

By visually sorting possible defect causes, identifying cause and effect relationships, and determining which causes are having the greatest impact on the problem, the Fishbone Diagram enables people to address the problem rather than its symptoms. It is frequently used to aid in lean and six-sigma transformations because it allows manufacturers to reduce clutter by identifying the root causes of issues and identify areas for improvement.

Getting started

The following steps will help you get started using a Fishbone Diagram for root cause analysis on your shop floor:

1. Identify the problem and write it in a box. This is the fish’s head. Draw an arrow leading into the head.

2. Brainstorm categories for potential causes and write them as branches from the arrow.

3. Brainstorm all potential causes and write them under the appropriate category (a cause might fall under more than one category). As you brainstorm, ask “why” each potential cause happens, and use these suggestions to generate more causes.

4. As you group the causes of the problem, it will become apparent which categories are having the largest effect on the problem. When you’ve finished brainstorming, prioritize the causes by how likely they are to be the cause of the problem and how easy they are to fix, focusing on the causes that are having the greatest effect on the problem.

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“Fishbone Diagram” also known as “Ishikawa diagram” and “Cause and Effect diagram.

It helps to Identify all potential or probable causes and select the best cause which contributes to the problem/effect.

The brainstorming technique is used here for potential cause identification.

In a brainstorming session, all 4M or 6M factors are taken into consideration to identify the potential causes.

4M or 6M factors are – Man, Machine, Method, Material, Measurement, and Mother nature also called Environment.

This is a very important basic 7 QC Tools and extensively used in Problem Solving Techniques like 8D, PDCA,and  Six Sigma.

• About Fishbone Diagram
• When to use an Ishikawa Diagram?
• Why use the Ishikawa Diagram?
  • Steps for making “Cause and Effect Diagram”
  • Benefits of “Fishbone Diagram“

• Developed by Kaoru Ishikawa of Japan.
• To find out probable or potential that contributes toproblem/effect.
• The brainstorming technique is used to identify potential causes.
• 4M or 6M factors analysis done in brainstorming.
• Helps to identify the root cause of the problem.

When to use an Ishikawa Diagram?

• Problem-solving to focus on the Quality problem.
• To sort out interactions among factors for a cause.
• To analyze existing problems.

Why use the Ishikawa Diagram?

• Helps to determine the Root Cause of a Problem.
• To identify the Key Inputs variables – Primary, Secondary and Tertiary causes.
• Helps in identifying the possible cause for variation present in a process.
• Increases knowledge of a process and its factors.
• Helps to identify areas for data collection.

Steps for making “Cause and Effect Diagram”

Step-1: Identify & define the problem/effect. Use 5W2H approach to define problem.

• Decide on the effect to examine.  

Step-2: Fill in the Problem Box & draw the spline.

Step-3: Identify main 4M or 6M categories/factors i.e. Primary causes.

Draw major cause categories and connect them to the “backbone” of the fishbone diagram.

Step-4: Identify Probable Causes that contributes to the problem/effects. Also called Secondary causes.

Use Brainstorming technique and Check sheet for cause analysis.

• Brainstorming – on 4M factors without previous preparation
• Check sheet – collected/recorded data for analysis

Step-5: Add detailed levels i.e. identify sub-causes & analyze the diagram. Also called Tertiary causes.

Benefits of “Fishbone Diagram“

• Focus is on ‘Causes’ rather than on ‘Symptoms’ or ‘assumptions’.
• Break problems down into small pieces to find the real root cause.
• Increase people involvement & teamwork.
• Improves team performance & effectiveness.
• Improves process knowledge.
• A common understanding of factors causing the problem.