Cause-and-Effect Diagram, Fishbone diagram or Ishikawa diagram
Fishbone diagram or Ishikawa diagram is one of the seven basic tools of Quality, first emphasized by Kaoru Ishikawa, a professor of engineering at Tokyo University and the father of “quality circles.”
Purpose of Fishbone diagram : To break down (in successive layers of detail) root causes that potentially contribute to a particular effect.
The fishbone will help to visually display as many as potential causes for a specific problem or effect.
Cause-and-effect diagram is also known as a fishbone diagram because of its shape, similar to the side view of a fish skeleton.
Benefits of using fishbone diagram :
• It identifies as many as possible causes for an effect or problem.
• It permit a thoughtful analysis
• It facilitates brainstorming.
• It helps maintain team focus
• It immediately sorts ideas into useful categories.
The causes are typical categorized into 5 Ms (used in manufacturing industry)
1 Machine (technology)
2 Method (process)
3 Material (Includes Raw Material, Consumables and Information)
4 Human Power (physical work)/Mind Power (brain work): Kaizens, Suggestions
5 Measurement/Medium (Inspection, Environment)
The causes are categorized into 8 Ps (used in product marketing industry)
7 Physical Evidence
The 5 Ss (used in service industry)
1 Surroundings RDp
4 Standard documentation skills
5 Scope of work
When to Use a Fishbone Diagram?
1 When identifying possible causes for a problem.
2 Discover the root cause for the problem.
3 To identify where & why the process isn’t working.
4 Especially when a team’s thinking tends to fall into ruts.
Fishbone Diagram Procedure (How to use the tool)
Step 1: Identify the Problem
First, write down the exact problem you face. Where appropriate, identify who is involved, what the problem is, and when and where it occurs.
Then, write the problem in a box on the left-hand side (some prefer writing problem on right-hand side)of a large sheet of paper, and draw a line across the paper horizontally from the box. This arrangement, looking like the head and spine of a fish, gives you space to develop ideas.
(It’s important to define your problem correctly.)
E.g Newspaper is delivered late on every Saturday
Step 2: Work Out the Major Factors Involved
Next, identify the factors that may be part of the problem. These may be systems, equipment, materials, external forces, people involved with the problem, and so on.
Try to draw out as many of these as possible. As a starting point, you can use models such as the 5 Ms, 8 Ps & 5 Ss Framework.
Then draw a line off the “spine” of the diagram for each factor, and label each line.
E.g.: taking the same problem of newspaper, the cause for the problem may be categorised into customer, process, Incentives, People, Budget, Environment, Method, Supplies.
Step 3: Identify Possible Causes
Now, for each of the factors you considered in step 2, brainstorm possible causes of the problem that may be related to the factor.
Show these possible causes as shorter lines coming off the “bones” of the diagram.
Where a cause is large or complex, then it may be best to break it down into sub-causes.
Brainstorm all the possible causes of the problem by using 5 Why.
• Ask: “Why does this happen?”
• Why does staff lack expertise? (Because we don’t attend training.)
• Why don’t we attend training? (Because we don’t have the funding.)
• Why don’t we have the funding? (Because we haven’t applied for grants.)
• Why don’t we apply for grants? (Because we’re unaware of sources.) etc.
this asking process is called the “Five Whys,” as five is often a manageable number to reach a suitable root cause. Your team may need more or less than five whys.
Again ask “why does this happen?” about each cause. Write sub–causes branching off the causes. Continue to ask “Why?” and generate deeper levels of causes. Layers of branches indicate causal relationships.
Step 4: Analyze Your Diagram
By this stage you have a diagram showing all of the possible causes of the problem that you can think of.
Depending on the complexity and importance of the problem, you can now investigate the most likely causes further. This may involve setting up investigations, carrying out surveys, and so on. These will be designed to test which of these possible causes is actually contributing to the problem.
The root causes of the event are the underlying process and system problems that allowed the contributing factors to culminate in a harmful event.
Lastly test for root causes by looking for causes that appear repeatedly within categories or across major categories.