1. Method Name

C&E Diagram (Cause and Effect)

2. Alternative Names

Ishikawa diagram (named after its creator, Kaoru Ishikawa), Fishbone diagram

3. Brief Description

An Ishikawa diagram is a visual tool for brainstorming and structured analysis that helps a team identify all possible causes of a specific problem (consequence). Its graphic form resembles a fish skeleton, where the “head” represents the problem and the “bones” represent the main categories of possible causes.

4. Purpose / When to Use

It is used in the analytical phase of problem-solving (e.g., the "Analyze" phase in DMAIC, the "Plan" phase in PDCA) to systematically examine all potential root causes. It is an excellent tool for team brainstorming that ensures no important area is overlooked.

5. Procedure / How to Apply It

1. Define the problem (Head of the Fish): On the right side of the paper or board, write down a clearly defined problem (consequence) and draw a thick line (“spine”) extending to the left from it.
2. Identify the main categories of causes (Main Bones): Draw diagonal lines extending from the “spine.” Each represents a single category. Traditional categories (especially in manufacturing) are the 6Ms
: - Man: factors related to people (training, fatigue, experience)
- Machine: equipment, tools,
maintenance- Method: procedures, instructions,
standards- Material: raw materials, parts, consumables-
Measurement: gauges, calibration,
definitions- Mother Nature/Environment: temperature, noise, culture
3. Brainstorming Causes (Smaller Bones): The team goes through each category one by one and generates ideas for specific causes that may have contributed to the problem. Each cause is written on a smaller “bone” attached to the corresponding main category.
4. Look for Deeper Causes: For each identified cause, ask “Why is this happening?” (use the 5 Whys technique) to drill down to the next level of detail and add even smaller “bones.”
5. Identify the most likely causes: After brainstorming is complete, the team discusses and votes (e.g., using Dot Voting) on which of the identified causes are the most likely and should be further validated using data.

6. A Real-World Example

Problem (head): Burnt pizza.
— Person: New cook, poor training, carelessness.
- Machine (oven): Incorrectly set thermostat, uneven baking, malfunctioning timer.
- Method: Incorrect recipe, unclear instructions, baking time too long by standard.
- Material: Dough too thin, different type of cheese (burns faster).
- Measurement: Inaccurate oven thermometer
.- Environment: Stress and rush during the lunch rush.

7. Benefits

- Structured brainstorming: Ensures that the team systematically considers all aspects of a problem
.- High team engagement: It is a visual and interactive method that engages the entire team.
- Focus on causes, not symptoms: Helps the team look beyond the obvious problems
.- Clear visualization: Creates a comprehensive overview of all possible causes in one place.

8. Risks / Limits

- It can be complex and confusing: If the team generates too many causes, the diagram may become unreadable
.- It is merely a list of opinions: The diagram itself does not verify which causes are valid. It is merely a list of hypotheses that must be further verified with data.
- Incorrect categorization: Causes may fall into multiple categories, which can lead to discussions that do not solve the problem.
- Superficiality: If the team does not use the 5 Whys to find deeper causes, the analysis will remain superficial.

9. Practical Tips

- The 6M categories are not set in stone: For administrative or service processes, other categories are often more appropriate, such as 4P (Policies, Procedures, People, Plant/Technology) or 4S (Surroundings, Suppliers, Systems, Skills).
- Let the diagram “live”: Prepare the diagram in advance and leave it in a visible place. Team members can add ideas gradually as they think of them.
- Combine it with a Pareto analysis: First, use the Pareto analysis to identify the main problem (e.g., “Burnt pizza is the most common complaint”), and then use the Ishikawa diagram to analyze its causes.