A Fishbone diagram, also known as an Ishikawa diagram or cause-and-effect diagram, is one of the seven basic quality control tools in Total Quality Management (TQM) used for root cause analysis. It's a visual tool for brainstorming and identifying the potential causes of a specific problem or effect.
Purpose and Function
The primary purpose of a fishbone diagram is to:
- Identify potential causes: Systematically explore and document all the factors that might be contributing to a specific problem.
- Analyze cause-and-effect relationships: Understand the relationships between different causes and their ultimate impact on the problem.
- Facilitate brainstorming: Encourage team collaboration in identifying and prioritizing potential causes.
- Focus problem-solving efforts: Direct improvement efforts toward addressing the root causes of a problem rather than just treating the symptoms.
Structure of a Fishbone Diagram
The diagram gets its name from its resemblance to a fish skeleton:
- The "Head" of the Fish: Represents the problem or effect you're trying to analyze.
- The "Spine" of the Fish: A horizontal line leading to the problem statement.
- The "Bones" of the Fish: Diagonal lines extending from the spine, representing the main categories of potential causes. Common categories include:
- Manpower: People involved in the process (e.g., training, skills, experience).
- Methods: Procedures and processes used (e.g., work instructions, documentation).
- Machines: Equipment and technology used (e.g., maintenance, calibration).
- Materials: Raw materials, components, and supplies (e.g., quality, availability).
- Measurement: Data collection and analysis (e.g., accuracy, reliability).
- Environment: External factors (e.g., temperature, lighting, workspace). These are often referred to as the 6Ms. Another common categorization used is the 8Ps, often used in marketing or service-related issues.
- Sub-Branches: Smaller lines branching off the main bones to represent specific causes within each category.
How to Create a Fishbone Diagram
- Define the Problem: Clearly state the problem or effect you want to analyze at the "head" of the fish.
- Identify Main Categories: Determine the main categories of potential causes. The 6Ms (Manpower, Methods, Machines, Materials, Measurement, and Environment) are a good starting point.
- Brainstorm Causes: For each category, brainstorm potential causes that could contribute to the problem. Ask "Why?" repeatedly to drill down to the root causes.
- Add Sub-Branches: Add sub-branches to the main bones to represent the specific causes.
- Analyze the Diagram: Review the completed diagram and identify the most likely root causes of the problem.
- Take Action: Develop and implement solutions to address the root causes.
Example
Let's say a manufacturing company is experiencing a high rate of product defects. A fishbone diagram can help them identify the potential causes:
- Problem: High product defect rate.
- Main Categories: Manpower, Methods, Machines, Materials, Measurement, Environment.
Under each category, the team would brainstorm specific causes:
- Manpower: Lack of training, insufficient skills, fatigue.
- Methods: Poor work instructions, inadequate quality control procedures.
- Machines: Malfunctioning equipment, improper calibration.
- Materials: Defective raw materials, incorrect specifications.
- Measurement: Inaccurate measuring tools, inadequate data collection.
- Environment: High humidity, poor lighting.
Benefits of Using Fishbone Diagrams in TQM
- Improved Problem Solving: Identifies root causes of problems.
- Enhanced Team Collaboration: Encourages teamwork and brainstorming.
- Visual Representation: Provides a clear visual overview of potential causes.
- Structured Approach: Offers a systematic approach to problem analysis.
- Focus on Prevention: Helps to prevent recurrence of problems by addressing their root causes.
