Cause and Effect/Fishbone Diagram

What is a Cause-and-Effect Diagram?

A Cause-and-Effect Diagram is an analysis tool that provides a systematic way of looking at effects and the causes that create or contribute to those effects. It was develop by Dr. Kaoru Ishikawa of Japan in 1943 and is sometimes referred to as an Ishikawa Diagram or a Fishbone Diagram because of its shape.

When should a team use a Cause-and-Effect Diagram?

Constructing a Cause-and-Effect diagram can help your team when you need to:

• Identify the possible root causes, the basic reasons, for a specific effect, problem, or condition.
• Sort out and relate some of the interactions among the factors affecting a particular process or effect.
• Analyze existing problems so that corrective action can be taken.

Why should we use a Cause-and-Effect Diagram?

A Cause-and-Effect Diagram is a tool that is useful for identifying for identifying and organizing the known or possible causes of quality, or the lack of it. The structure provided by the diagram helps team members think in a very systematic way. Some of the benefits of constructing a Cause-and-Effect Diagram are that it:

• Helps determine the root causes of a problem or quality characteristic using a structured approach.
• Encourages group participation and utilizes group knowledge of the process.
• Uses an orderly, easy-to-read format to diagram cause-and-effect relationships.
• Indicates possible causes of variation in a process.
• Increases knowledge of the process by helping everyone to learn more about the factors at work and how they relate.
• Identifies areas where data should be collected for further study.

How do we develop a Cause-and-Effect Diagram?

When you develop a Cause-and-Effect Diagram, you are constructing a structured, pictorial display of a list of causes organized to show their relationship to a specific effect. See Viewgraph 1. Notice that the diagram has a cause side and an effect side.

The steps for constructing and analyzing a Cause-and-Effect Diagram are outlined below.

Step 1 Identify and clearly define the outcome or EFFECT to be analyzed.

• Decide on the effect to be examined. Effects are stated as particular quality characteristics, problems resulting from work, planning objectives, and the like.
• Use Operational Definitions. Develop an Operational Definition of the effect to ensure that it is clearly understood.
• Remember, an effect may be positive (an objective) or negative (a problem), depending upon the issue that's being discussed.
  • Using a positive effect which focuses on a desired outcome tends to foster pride and ownership over productive areas. This may lead to an upbeat atmosphere that encourages the participation of the group. When possible, it is preferable to phrase the effect in positive terms.
  • Focusing on a negative effect can sidetrack the team into justifying why the problem occurred and placing blame. However, it is sometimes easier for a team to focus on what causes a problem than what causes an excellent outcome. While you should be cautious about the fallout that can result from focusing on a negative effect, getting a team to concentrate on things that can go wrong may foster a more relaxed atmosphere and sometimes enhances group participation.

You must decide which approach will work best with your group.

Step 2 Using chart pack positioned so that everyone can see it, draw the SPINE and create the EFFECT box.

• Draw a horizontal arrow pointing to the right. This is the spine.
• To the right of the arrow, write a brief description of the effect or outcome which results from the process.
  EXAMPLE: The EFFECT is Late Pizza Delivery. See Viewgraph 2.
• Draw a box around the description of the effect.

Step 3 Identify the main CAUSES contributing to the effect being studied.

These are the labels for the major branches of your diagram and become categories under which to list the many causes related to those categories.

• Establish the main causes, or categories, under which other possible causes will be listed. You should use category labels that make sense for the diagram you are creating. Here are some commonly used categories:
  • 3Ms and P - methods, materials, machinery, and people
  • 4Ps - policies, procedures, people, and plant
  • Environment - a potentially significant fifth category
• Write the main categories your team has selected to the left of the effect box, some above the spine and some below it.
• Draw a box around each category label and use a diagonal line to form a branch connecting the box to the spine.
  EXAMPLE: Viewgraph 3 uses the 3Ms and P to start developing the diagram we began in Step 2.

Step 4 For each major branch, identify other specific factors which may be the CAUSES of the EFFECT.

• Identify as many causes or factors as possible and attach them as sub-branches of the major branches.
  EXAMPLE: The possible CAUSES for Late Pizza Delivery are listed under the appropriate categories in Viewgraph 4.
  
  
• Fill in detail for each cause. If a minor cause applies to more than one major cause, list it under both.

Step 5 Identify increasingly more detailed levels of causes and continue organizing them under related causes or categories. You can do this by asking a series of why questions.

EXAMPLE: We'll use a series of why questions to fill in the detailed levels for one of the causes listed under each of the main categories.

Q: Why was PEOPLE DON'T SHOW UP?
A: There is no teamwork
     Q: Why there is no teamwork?
     A: No training

A: High turnover
     Q: Why high turnover?
     A: Low pay

Q: Why was the OVEN TOO SMALL?
A: No capacity for peak periods
A: Poor use of space
     Q: Why poor use of space?
     A: Poor training

Q: Why was HANDLING OF LARGE ORDERS POOR?
A: Lack of experience
     Q: Why was experience lack?
     A: High turnover

Q: Why was DISPATCHING POOR?
A: Don't know town
     Q: Why wasn't town known?
     A: High turnover

Q: Why was INGREDIENTS RUN OUT?
A: Inaccurate ordering
     Q: Why was ordering inaccurate?
     A: High turnover
     A: Poor use of space
          Q: Why poor use of space?
          A: Lack of training

Viewgraph 5 shows how the diagram looks when all the contributing causes that were identified by the series of why questions have been filled in. As you can see, there may be many levels of causes contributing to the effect.

Note: You may need to break your diagram into smaller diagrams if one branch has too many sub-branches. Any main cause (3Ms and P, 4Ps, or a category you have named) can be reworded into an effect.

Step 6 Analyze the diagram.

Analysis helps you identify causes that warrant further investigation. Since Cause-and-Effect Diagrams identify only possible causes, you may want to use a Pareto Chart to help your team determine the cause to focus on first.

• Look at the "balance" of your diagram, checking for comparable levels of detail for most of the categories.
  • A thick cluster of items in one area may indicate a need for further study.
  • A main category having only a few specific causes may indicate a need for further identification of causes.
  • If several major branches have only a few sub-branches, you may need to combine them under a single category.
• Look for causes that appear repeatedly. These may represent root causes.
• Look for what you can measure in each cause so you can quantify the effects of any changes you make.
• Most importantly, identify and circle the causes that you can take action on.
  EXAMPLE: Let's analyze the diagram we have been constructing.
  • The level of detail is pretty well balanced.
  • The causes Poor/No Training, High Turnover are repeated.
  • No Training and High Turnover appears to be the causes for which you could develop measurements.
  • Moreover, No Training and High Turnover appear to be the causes that you can take action on. It is circled in Viewgraph 5 to earmark it for further investigation.