Blog 5: How to use Fishbone diagram to find the root cause?

Introduction:

Cause and Effect diagrams, also referred to as Fishbone diagrams, are a quality control brainstorming tool used to help identify the root cause or causes of an issue by looking at all possible variables. This tool was designed by Dr. Kaoru Ishikawa hence this tool is also called as Ishikawa diagram. It was developed in 1943.

When using these diagrams, a central issue or focal points, such as a defect or quality problem, is placed at the head of the “fish.” The “bones of the fish” serve as a way to visually organize all possible variables or causes, that may have caused the central issue, and sort ideas into categories to investigate further.

Cause–and–effect diagram helps in identifying the various causes (or factors) leading to an effect (or problem) and also helps in deriving meaningful relationships between them.

The very purpose of this diagram is to identify all the root causes behind a problem.

Once a quality-related problem is defined, the factors leading to the cause of the problem are identified. We further keep identifying the sub-factors leading to the causal of identified factors till we are able to identify the root cause of the problem. As a result, we get a diagram with branches and sub-branches of causal factors resembling to a fishbone diagram.

How to make a Cause and Effect chart.

1. State the undesirable effect or problem: To start with the cause and effect diagram, make all the lines that look like a backbone of a fish.  On the right side of the fishbone right the major effect for which the cause and effect diagram is being made.
2. Identify the main cause group: Next we go for the cause. To identify the cause we use the 6M method i.e
   • Man
   • Methods
   • Machines
   • Material
   • Measurements
   • Mother Nature

For different effects and different jobs, different formulae are used.

• Arrange the cause and sub-causes as relevant: Now after noting each of the categories we think of subcategories that can go inside each of the relevant causes.
• Identify potential root cause: Now we start with the why why analysis. Since we know the category of each cause we now as ourselves why and provide the answer then we ask next why till we find the root cause of the problem. That root cause is noted.

Uses of Cause-and-Effect Diagram

There are various uses of the cause-and-effect diagram:

• We can use it in problem-solving and finding the root causes of an issue.
• Gathering different perspectives on the case during the group brainstorming session.
• Exposing the association between various reasons leading to an issue.
• Cause-and-Effect diagram finds the issue area which required to be examined and writes it at the top of the diagram.
• Find out the core reasons for the problem. These are the tags for the key branches of the fishbone diagram. These main categories comprise material, machinery, methods, procedures, policies, people, etc.
• Identify probable sub-cases of the main causes and join them as sub-branches of the main branches.
• Examine the major and minor causes in-depth; refer to the diagram we created.
• When we identify the root cause, make an action plan outlining our strategy in order to overcome the problem.

Advantages:

• There are various advantages of the Cause-and-Effect diagram:
• It encourages group participation
• Increases process knowledge
• With the help of it, we can determine the root causes.
• Shows possible causes of variation.
• Find out the areas for collecting.

Disadvantages:

• There are various disadvantages of the cause-and-effect diagram:
• It requires expertise and skills.
• Democratic selection of causes.
• Lack evidence
• Overemphasis gives irrelevant outcomes
• Multiple root causes
• Wastage of time and effort on unrelated causes.
• Tough to depict complex correlations among causes.

Example of Cause and Effect diagram.