Tuesday, 22 July 2014

Fish Bone Diagram – A Tool For Root Cause Analysis

Fish Bone Diagram – A Tool For Root Cause  Analysis

Fish bone diagram is a brain storming tool used to identify the root cause of a problem. The design of the diagram looks much like the skeleton of a fish. Dr. Kaoru Ishikawa, a Japanese quality control statistician, invented the fish bone diagram. Therefore, it is referred as Ishikawa diagram. The fish bone diagram is an analysis tool that provides a systematic way of looking at effects and the causes that create or contribute to those effects. Because of its function it may be referred to as a cause-and-effect diagram.

                                         Dr. Kaoru Ishikawa

Fish Borne Diagram is basically used to investigate a problem, exploring, identifying, and displaying the possible causes.

-   Head of a Fish: Problem or Effect
-   Horizontal Branches: Primary Cause
-   Sub – Branches : Secondary cause

In the diagram, the various causes are grouped into categories (such as equipment, materials or processes) and the arrows in the image indicate how the causes cascade or flow toward the non-conformity.

The categories are not pre-defined but common ones include:
·       Equipment – this should include consideration of all equipment that could have a role in the non-conformity, for example, production line, facilities, computers or tools
·       Processes or Methods – how work is performed, policies, procedures, rules or work instructions
·       Materials – any information relating to raw materials or final products, for example raw material specification or goods receipt checks for a specific batch of ingredient.
·       Environment – The location, time, temperature, culture, standards of cleanliness or available time, for an activity.
·       People – Any role involved in the implicated process.

A cause-and-effect analysis generates and sorts hypothesis about possible causes of problems within a process by asking participants to list all of the possible causes and effects for the identified problem. Cause-and-effect diagrams can reflect either causes that block the way to the desired state or helpful factors needed to reach the desired state.

How is it done?

  •  Name the effect; determine the specific problem to be analyzed. Draw the diagram with a process arrow to the effect and draw a box around it.

  • Decide what the major categories of the causes are (i.e., people, machines, measurement, materials, methods, environment, policies, etc.).

  •  Label categories important to your situation. Make it work for you.

  • Brainstorm all possible causes and label each cause under the appropriate category.

  • Post the diagram where others can add causes to it (i.e., experts, affected people, process owners, etc..).

  • Analyze causes and eliminate trivial and/or frivolous ideas.

  • Rank causes and circle the most likely ones for further consideration and study.

  •  Investigate the circled causes. Use other techniques to gather data and prioritize findings.


  • Cause and effect analysis identifies core problems.

  • Whenever multiple possible explanations exist for a single issue, root cause analysis enables the team to better understand the issues and prioritize their improvement efforts.

  • Generates a large quantity a variable ideas in a short space of time.


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  3. one of a basic tool of six sigma methodology

  4. one of a basic tool of six sigma methodology