A Cause and Effect Diagram, also known as a Fishbone or Ishikawa diagram, is a powerful visual tool used in the Measure Phase of Lean Six Sigma to identify and organize potential causes of a specific problem or effect. Named after Japanese quality expert Kaoru Ishikawa, this diagram resembles a fis…A Cause and Effect Diagram, also known as a Fishbone or Ishikawa diagram, is a powerful visual tool used in the Measure Phase of Lean Six Sigma to identify and organize potential causes of a specific problem or effect. Named after Japanese quality expert Kaoru Ishikawa, this diagram resembles a fish skeleton, with the problem statement placed at the head and contributing factors branching off like bones along the spine.
The diagram typically organizes potential causes into major categories, commonly remembered using the 6Ms: Man (People), Machine (Equipment), Method (Process), Material, Measurement, and Mother Nature (Environment). For service industries, alternative categories might include Policies, Procedures, People, and Place.
To create a Fishbone diagram, teams first clearly define the problem or effect being analyzed and place it in a box on the right side. A horizontal line extends from this box, forming the spine. Major category branches are then drawn at angles from the spine. Through brainstorming sessions, team members identify potential causes within each category, adding them as smaller branches.
The primary benefits of using Cause and Effect Diagrams include facilitating structured brainstorming, encouraging team participation, providing a visual representation of complex relationships, and helping teams move beyond symptoms to identify root causes. This tool promotes systematic thinking and ensures comprehensive analysis by examining multiple categories of potential causes.
During the Measure Phase, Fishbone diagrams help teams understand what factors might be influencing process variation or defects. The identified causes can then be validated through data collection and analysis. This structured approach ensures that improvement efforts focus on addressing actual root causes rather than just treating symptoms, leading to more sustainable solutions and measurable improvements in process performance.
Cause and Effect Diagrams (Fishbone/Ishikawa) - Complete Guide
Why Cause and Effect Diagrams Are Important
Cause and Effect Diagrams, also known as Fishbone Diagrams or Ishikawa Diagrams, are essential tools in the Measure Phase of Six Sigma. They help teams visually identify, explore, and display all possible causes of a specific problem or effect. This structured approach prevents teams from jumping to conclusions and ensures a thorough root cause analysis.
What Is a Cause and Effect Diagram?
A Cause and Effect Diagram is a visual tool that resembles a fish skeleton. The head of the fish represents the problem or effect being analyzed, while the bones branching off the spine represent categories of potential causes. Sub-causes branch off from these main category bones, creating a comprehensive map of all factors that might contribute to the problem.
The diagram was developed by Dr. Kaoru Ishikawa in the 1960s, which is why it bears his name. It is one of the Seven Basic Quality Tools used in process improvement.
How It Works
1. Define the Problem: Write the problem statement or effect at the head of the fish on the right side of the diagram.
2. Identify Major Categories: Draw the main bones extending from the spine. Common categories include the 6 Ms: - Man (People) - Machine (Equipment) - Method (Process) - Material (Inputs) - Measurement (Data collection) - Mother Nature (Environment)
3. Brainstorm Causes: For each category, brainstorm potential causes and add them as smaller bones branching off the main category bones.
4. Analyze Further: Ask Why? repeatedly to drill down into sub-causes, adding these as even smaller branches.
5. Prioritize: Once complete, use data and team consensus to identify the most likely root causes for further investigation.
Key Benefits
- Encourages team brainstorming and collaboration - Provides a structured framework for analysis - Helps visualize relationships between causes and effects - Prevents overlooking potential contributing factors - Creates documentation for future reference
Exam Tips: Answering Questions on Cause and Effect Diagrams
Tip 1: Remember the alternative names. Questions may refer to Fishbone Diagram, Ishikawa Diagram, or Cause and Effect Diagram interchangeably.
Tip 2: Memorize the 6 Ms categories. Exam questions often ask you to identify appropriate categories or select which M a specific cause belongs to.
Tip 3: Understand when to use this tool. It is primarily used during the Measure and Analyze phases for identifying potential causes before data collection and analysis.
Tip 4: Know that the diagram displays potential causes, not confirmed root causes. Verification through data analysis is still required.
Tip 5: Be prepared to identify the correct placement of causes within categories when shown a diagram.
Tip 6: Remember that this is a qualitative brainstorming tool, not a statistical analysis method.
Tip 7: Questions may ask about the sequence of steps. Know that defining the problem comes first, followed by identifying categories, then brainstorming causes.
Tip 8: Recognize that Fishbone Diagrams work well in combination with other tools like the 5 Whys technique and brainstorming sessions.