The Fishbone Diagram, How to Use it in Six Sigma

The "fishbone diagram" is a problem-solving tool used in Six Sigma projects to identify the root causes of a problem. It is also known as an Ishikawa diagram or a cause-and-effect diagram.

But, how exactly does it work?

Problem statement:

A restaurant is experiencing a high rate of customer complaints regarding the quality of the food.

Fishbone diagram process:

The restaurant team uses a fishbone diagram to identify the root cause of the problem.

1. Draw the head of the fish: 
   The head of the fish represents the problem or effect. In this case, the head would be "high rate of customer complaints regarding the quality of the food".
2. Draw the spine of the fish: 
   The spine of the fish represents the main categories of potential causes. In this case, the categories could be equipment, people, process, environment, and materials.
3. Draw the bones of the fish: 
   The bones of the fish represent the subcategories of potential causes within each main category. For example, under the equipment category, the bones could include kitchen appliances, cooking utensils, and food storage containers. Under the people category, the bones could include cooks, waitstaff, and management.
4. Identify potential causes: 
   The team brainstorms potential causes for each subcategory and writes them on the corresponding bone. For example, under the kitchen appliances bone, potential causes could include broken ovens, malfunctioning stovetops, and inadequate refrigeration. Under the cooks bone, potential causes could include lack of training, insufficient staffing, and poor communication.
5. Analyze the causes: 
   The team analyzes each potential cause to determine whether it is a root cause or a symptom of a deeper issue. They may use additional tools, such as data analysis or surveys, to validate their findings. For example, they may find that the root cause of the complaints is a lack of training for the cooks, which leads to inconsistent quality and incorrect orders.
6. Develop solutions: 
   Based on the analysis, the team develops solutions to address the root cause. In this case, they may develop a training program for the cooks to ensure they are properly trained on food preparation and quality control measures.
7. Implement and monitor: 
   The team implements the solutions and monitors the results to ensure that the problem is solved and does not recur. They may use additional tools, such as process control charts, to track the effectiveness of the solutions over time.

In this way, the fishbone diagram helps the team identify the root cause of the problem and develop targeted solutions to address it.