Carillon Technologies Limited  Cause-And-Effect Diagrams

Introduction

After a problem has been identified through the use of a Quality Cost study and a Pareto analysis , you next need to determine the possible causes. An excellent tool for doing this is the cause-and-effect diagram.

The cause-and-effect diagram is sometimes called a fishbone chart because it looks like the skeleton of a fish. Since it was developed by Dr. Kaoru Ishikawa of the University of Tokyo in the 1950's, it is also referred to as an Ishikawa diagram.

What is a cause-and-effect (fishbone) chart? The cause-and-effect chart is a graphical aid that lists the factors that cause variation in a process.

The diagram starts with the problem and then works backwards to all the possible causes of the problem.

Why is a cause-and-effect chart used?

1. To determine the most likely causes of the problem.

The cause-and-effect chart provides graphical representation of the possible causes of process variation and their interaction. It reveals the most likely causes, which can be tested for their effect upon the problem.

2. To document the team's understanding of the problem.

STEPS FOR CONSTRUCTING A CAUSE-AND-EFFECT DIAGRAM

Step #1 Define the problem to be studied.

The problem is usually identified through the use of the Pareto analysis technique.

Make sure that the problem is well defined.

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Step #2 Construct a line from left to right, ending at a box which lists the problem or effect.

Our example studies burnt corn flakes.

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Step #3 Identify the major causes of the problem.

Write the names of these major causes or factors at the ends of the main branches. The causes could include worker, machine, material, environment, method, management, or measurement.

Caution: Write down only the causes of the problem. Do not jump to the solution. Many valuable ideas will be lost and the most probable cause might be lost.

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Step #4 Brainstorm for the possible causes of the problem.

Step #5 Evaluate Ideas.

From all the ideas, choose those that tie in with the major causes listed on the cause-and-effect diagram.

These ideas will be used to develop the diagram. The evaluation step can involve:

1. Clarifying ideas

2. Combining similar ideas.

3. Removing ideas that don't belong.

Another good tool for developing ideas is the"Five Why's."

The ideas that resulted from the brainstorming session and the five why's are now applied to the cause-and-effect chart, as shown below.

The following chart shows a complete cause-and-effect diagram.

Step #6 Vote for the most likely causes.

• Members of the group vote for those items that they think are the most likely cause of the problem.
• The number of votes is completely open. Each member votes for his or her most likely cause or causes.
• The number of votes each item receives is marked on the chart next to the idea.
• This step completes the actual cause-and-effect chart.

Completed Cause-and-Effect Chart with votes:

Step #7 Rank the causes by frequency.

This chart shows that the top five most likely causes are:

Cycle time	6 votes
Thermostat	6 votes
Temperature of the drying air	5 votes
Burner	4 votes
Thickness of the corn flake	4 votes

Step #8 Verify the results

• To verify the results you must collect data by using the appropriate check sheet.
• And then analyze the results for supporting evidence that you picked the appropriate cause.

Step # 9 Take corrective action on cause(s) that produced the problem.

Different Types of Cause-and-Effect Diagrams

There are variations of the basic cause-and-effect diagram that we just studied. The method we just studied is called

• Cause enumeration

Other forms include:

• Process analysis cause-and-effect
• Solution analysis cause-and-effect

Conclusions

The cause-and-effect charts are effective problem-solving tools that can be used in conjunction with other analysis tools to pinpoint potential causes of the problem.

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