Define Cause and Effect Diagram

What is a Cause and Effect Diagram?

A Cause and Effect Diagram is a visual tool used to explore and identify the potential causes of a particular problem or quality issue within a process. Created by Japanese quality control expert Kaoru Ishikawa in the 1960s, this diagram is aptly named the “Ishikawa Diagram” in his honor. Its appearance resembles the skeletal structure of a fish, hence the alternative name “Fishbone Diagram.”

The diagram provides a structured approach to root cause analysis by breaking down a problem into its various contributing factors. These factors are categorized into primary branches that resemble the bones of a fish, with the problem statement placed at the head of the fish.

Each branch represents a potential category of causes that could be contributing to the problem, such as people, methods, machines, materials, measurements, and environmental factors. Subsequently, sub-branches or “fishbones” extend from each primary branch, further detailing specific causes within each category.

How Are Cause and Effect Diagrams Used in Six Sigma Projects?

In Six Sigma projects, Cause and Effect Diagrams are a valuable tool for several reasons:

1. Problem Identification and Clarification:

The initial step in any Six Sigma project is accurately defining the problem. Cause and Effect Diagrams help project teams brainstorm and identify all potential causes and contributors to the problem, ensuring a comprehensive understanding of the issue at hand. This clarity is essential for effective problem-solving.

2. Root Cause Analysis:

Determining the root cause(s) of a problem is a fundamental aspect of Six Sigma. Project teams can systematically investigate each potential contributor by structuring causes into categories and sub-categories on the Fishbone Diagram. This methodical approach facilitates a deeper analysis, enabling teams to pinpoint the true root cause of the problem rather than addressing symptoms or secondary issues.

3. Data Collection and Analysis:

Cause and Effect Diagrams are often used in conjunction with data collection. Once potential causes are identified, teams can collect data to assess their significance and impact on the problem. Statistical tools and techniques, such as Pareto charts or hypothesis testing, can be employed to prioritize and validate these potential causes.

4. Brainstorming and Team Collaboration:

Six Sigma projects often involve cross-functional teams, and the collaborative nature of the cause-and-effect diagram encourages brainstorming and idea-sharing. Team members from different backgrounds can contribute their insights and perspectives, leading to a more comprehensive analysis.

5. Continuous Improvement:

Six Sigma is not just about solving immediate problems but also about preventing their recurrence. Cause and Effect Diagrams help teams develop effective solutions and preventive measures. By addressing root causes, organizations can enhance their processes, reduce defects, and achieve lasting improvements.

Limitations with using Cause and Effect Diagrams During a Project:

While Cause and Effect Diagrams are valuable tools for root cause analysis in various projects, they are not without their limitations. Here are some problems and potential drawbacks associated with using Cause and Effect Diagrams during a project:

  1. Overcomplication: Cause and Effect Diagrams can become overly complex, especially in projects with multifaceted problems. When too many potential causes and sub-causes are identified, it can be challenging to prioritize and focus on the most critical factors.

  2. Subjectivity: The process of brainstorming and categorizing causes in the diagram can introduce subjectivity. Different team members may have varying opinions on the significance of certain causes, leading to potential biases in the analysis.

  3. Lack of Quantification: Cause and Effect Diagrams are qualitative tools, which means they do not provide quantitative data on the impact or importance of each cause. This can make it difficult to prioritize causes based on their actual contribution to the problem.

  4. Limited to Known Causes: These diagrams are most effective when the team already has some knowledge of the potential causes. In situations where the causes are entirely unknown or unexpected, the diagram may not be as useful.

  5. Time-Consuming: Constructing a comprehensive Cause and Effect Diagram can be time-consuming, particularly in complex projects. This may delay problem-solving efforts, especially when a quick resolution is required.

  6. Focus on Symptoms: Teams can sometimes address symptoms rather than root causes, especially if they do not thoroughly investigate each branch of the diagram. This can lead to temporary solutions that do not prevent problem recurrence.

  7. Ineffectiveness in Complex Processes: In very intricate or nonlinear processes, creating a meaningful Cause and Effect Diagram that accurately represents the relationships between causes and effects may be challenging.

  8. Neglecting Interactions: The diagram often assumes that causes are independent, but in reality, causes can interact with one another in complex ways. This oversimplification may lead to incomplete or inaccurate conclusions.

  9. Resistance to Change: In some cases, employees or team members may resist the changes suggested by the analysis of a Cause and Effect Diagram, especially if they perceive these changes as disruptive to established routines or practices.

  10. Limited Scope: Cause and Effect Diagrams are most effective for isolated problems within a specific process. They may not be suitable for addressing broader organizational issues or strategic challenges.

  11. Inadequate Data: The effectiveness of a Cause and Effect Diagram relies on the availability of accurate and relevant data. If data is incomplete, unreliable, or unavailable, it can hinder the analysis and the identification of root causes.

  12. Lack of Follow-Up: Creating a Cause and Effect Diagram is just the beginning of the problem-solving process. Without effective follow-up and action plans, the diagram can become an academic exercise with no practical impact on improving processes.

Despite these potential problems, Cause and Effect Diagrams remain valuable when used judiciously and with other problem-solving and data analysis techniques. To mitigate these challenges, project teams need to maintain a critical and objective perspective, actively seek diverse input, and validate their findings through further data analysis and experimentation.


Cause and Effect Diagrams are vital in the Six Sigma toolkit. They assist in problem identification, root cause analysis, data-driven decision-making, and collaborative problem-solving. When employed effectively, these diagrams empower organizations to eliminate defects, optimize processes, and enhance overall quality, ultimately contributing to their pursuit of perfection in process improvement.