A cause and effect diagram is a visual tool used to logically organize the possible causes of a specific problem or effect by graphically displaying them in greater detail, suggesting causal relationships between theories. A popular type is also known as a fishbone or Ishikawa diagram. The cause-effect model can also be diagnosed using a tree diagram.
When diagnosing the cause of a problem, a cause and effect diagram helps organize various theories about the root causes and presents them graphically. It is a relevant tool in the early stages of team improvement. Ideas generated during brainstorming or affinity processes are used to complete the diagram.
Since the list of problems in a cause and effect diagram can be quite large, the team should use a prioritization technique or multiple voting to reduce the list of possible causes to be further investigated.
At the head of the diagram is the effect that the team is investigating, with the possible causes of this effect branching out. The branches represent potential causes, and the headers are the column headers of the affinity diagram.
A cause and effect diagram is generally prepared as a prelude to developing the necessary data to empirically establish causality.
A cause and effect diagram cannot identify a root cause; it graphically presents the many causes that may contribute to the observed effect. It is a visual representation of factors that could contribute to an observed effect being examined. Interrelationships among possible causal factors are clearly shown. A causal factor may appear in multiple places on the diagram. Interrelationships are generally qualitative and hypothetical. It focuses the attention of all team members on the specific problem in a structured and systematic way.
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The cause and effect diagram is constructed using these 5 factors:
Environment: The environmental conditions that impact the process, such as time, temperature, humidity, and cleanliness. Human factor: Involves anyone who collaborates throughout the supply chain process, including all support functions.
Method: Specifies how the process is performed and what requirements are necessary, such as quality procedures, work orders, instructions, or blueprints.
Machinery: Includes all machines and equipment required to perform a specific task.
Materials: Raw materials, purchased materials, and everything that constitutes the manufacturing of a final product.
There are several advantages to cause and effect diagrams that help visualize problems and their causes to compare relevant solutions.
The main advantage of this tool is that it focuses the attention of all individuals involved in the specific problem in a systematic and structured manner. It encourages innovative thinking while keeping the team on track in an organized way.
The second strength of this tool is that its graphical representation allows for the manifestation of complex situations, showing clear relationships between elements. When a problem is potentially affected by complex interactions among many causes, the cause and effect diagram provides the means to document and organize them all.
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A cause and effect diagram is constructed when theories can be developed to guide the characterization step. The knowledge to build the cause and effect diagram comes from people familiar with the problem and the data that has been collected so far.
Clearly define the effect or symptom for which the causes need to be identified. The "effect" should be defined in writing. For clarity, it may be advisable to explain in detail what is included and what is excluded.
If the effect is too general of a statement, different people involved will interpret it in very different ways. Contributions will then tend to be diffuse rather than focused. They may provide considerations that are irrelevant to the specific problem.
Brainstorming or a rational step-by-step approach can be used to identify possible causes. There are two possible approaches to gather contributions for the causes that will be placed on the diagram: brainstorming and a rational step-by-step approach. The team or its leadership should make a decision based on an assessment of readiness.
Brainstorming would typically be indicated for a team with a few people who may dominate the conversation in a destructive way or for a team with a few people who may be excessively reserved and not contribute. Additionally, brainstorming may be better for addressing very unusual problems where creativity is prioritized.
If team members are prepared to work in that environment, a step-by-step approach will generally produce a final product in less time, and the quality of the proposed causal relationships will normally be better.
In the step-by-step procedure, you should start by identifying the main causes or classes of causes that will be placed in the boxes at the ends of the main branches coming off the central column of the diagram.
Each of the main causes (not less than two and usually not more than six) should be written in a box and connected to the central column by a line at an angle of about 70 degrees.
It is advisable to add causes for each main branch. Each factor that causes a main branch is placed at the end of a line that is drawn to connect with the appropriate main branch line and is parallel to the central column.
A root cause has three characteristics that will help explain when to stop. First, it triggers the event the team was seeking, either directly or through a sequence of intermediate causes and effects. Secondly, it is directly controllable. That is, in principle, team members could intervene to change that cause.
Check the logical validity of each causal chain. Once the entire fishbone diagram is completed, it is advisable to start with each potential root cause and "read" the diagram forward to the effect it explains. Ensure that each causal chain makes logical and operational sense.
Finally, check that the causal chain is adequately connected between the root cause and the sequence of causes that stem from it. From there, the diagram should be complete, and the problem identified along with its potential effects or consequences. This will allow the team to work on the identified problem in a well-directed manner, generate relevant solutions, and achieve the expected results.
The primary application of cause and effect diagrams is for the organized arrangement of theories about the causes of the observed quality problem that the team needs to address. Once the theories are well understood and organized, the team will use its collective judgment to identify those theories that need testing. The ultimate goal of the characterization step is to identify the root cause or main causes of the team's problem.
A cause and effect diagram can sometimes be useful for systematically thinking about the resistance that the proposed solution is likely to encounter. If the phenomenon to be explained is resistance to the proposed remedy, then the team can construct a cause and effect diagram to help identify the most important resistances that need to be addressed.
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The cause and effect diagram is a highly useful tool for visually identifying the possible causes and effects of a specific problem. Its visibility contributes to the process of developing actions aimed at providing effective solutions that eliminate the problem from its root cause.
While it may seem somewhat rudimentary and outdated, nowadays there are technological options that can even create and replicate these diagrams, incorporating all their connections and the relevant information from the conclusions established during the problem analysis.