Cause and Effect diagram in 7 QC tools?

Cause and Effect Diagram

A cause and effect diagram is a graphical tool to identify possible causes of a problem or effect. It is one of the basic tools of 7 QC Tools.

The cause and effect diagram analysis was first developed by Professor Kaoru Ishikawa of Japan in 1960. The cause and effect diagram is also known as the ‘Fishbone Diagram’ and ‘Ishikawa  Diagram

The cause and effect diagram identifies many possible causes for an effect or problem. It can be used to structure a brainstorming session by the CFT, QC team having process knowledge. It immediately sorts ideas into useful categories. It helps to identify the root cause of the problem.

When to use Fishbone Diagram?

  • When exploring all possible causes of a problem.
  • When identifying potential causes for a problem.
  • To find out the relationship between effect and related factors.
  • To analyze big problems after doing Pareto analysis.

Cause and Effect Diagram Procedure :

  • Define a problem statement.
  • Write it at the center-right of the paper or board.
  • Draw a box around it and then draw a horizontal arrow running to it
  • Brainstorm the major categories of causes of the problem.
  • Write the categories of causes as branches from the main arrow.
  • When you are brainstorming causes,  consider having team members write each cause on sticky notes, going around the group asking each person for one cause.  Ask: “Why does this happen?”

Write sub-causes branching off the causes. Continue going through the rounds, getting more causes, until all ideas are exhausted. Causes can be written in several places if they relate to several categories.

  • Analyze causes and eliminate trivial ideas.
  • Rank causes and circles the most likely ones for further consideration and study.
  • Investigate the potential circled causes. Simulate those potential causes for actual happening. If it is found valid. Then do a Why Why Analysis on the potential cause to find out the actual root cause.

6M in cause and effect diagram:

  • Manpower
  • Machines
  • Methods
  • Materials
  • Measurement
  • Management / Environment

Cause and Effect diagram example:

This is an example of a cause-and-effect diagram of the bending out the problem in sheet metal parts.

Cause and Effect Diagram

What is the use of a cause & effect diagram?

  • Breaks problems down into small parts to find the root cause.
  • Encourage team participation & knowledge sharing.
  • The common understanding of factors causing the problem.
  • Road map to verify the flow of the process.
  • Follows brainstorming relationship.
  • Indicates possible causes of variation.
  • Increases process knowledge.
  • It demonstrates knowledge of the problem-solving team.
  • The diagram is a guide for data collection.
  • It helps to find out the root cause of a problem.
  • It focuses on causes rather than symptoms.

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