What Is a Fishbone Diagram?

A fishbone diagram, also known as a cause-and-effect diagram or an Ishikawa diagram, is a helpful tool for identifying the root cause of a problem. It allows you to list all the potential causes that may be contributing to the effect you are currently experiencing. This visual aid, which takes the shape of a fishbone, hence its name, is commonly used during brainstorming sessions.

To create a fishbone diagram, you organise the possible causes on the left side, categorised under different cause categories. These make up the "bones" of the fish. On the right side, you place the effect or problem you are investigating–the "head." This structure provides a quick and easy way to visualise the various causes associated with the effect.

How to create a fishbone diagram

The following offers a step-by-step approach to help you construct a fishbone diagram: 

1. Provide a problem statement. 

A problem statement is the effect or problem you are investigating. It is placed in a box with an arrow pointing to it on the right side of a flipchart page as if forming the head of a fish. Everyone on the team agrees on the definition of the problem.  

2. Define major cause categories. 

Form the skeleton of your fishbone diagram with the major cause categories, which you connect to the backbone. To find these categories, have a brainstorming session with your team. The number of categories you create will vary according to your industry and the problem you’re solving. For example, if you work in manufacturing, your major cause categories may be staff/people, equipment and machinery, processes and procedures, materials, environmental factors, and measuring procedures.

3. Brainstorm causes. 

Now that you have your major cause categories in place, take time to brainstorm possible causes. You can use the categories to generate ideas or list as many causes as you can think of as a team.

4. Categorise causes. 

Go through your list of causes and add them to the appropriate category on your diagram. These causes become the ribs on your diagram, joining categories to the backbone. 

5. Discover sub-causes. 

For each cause you identify, go deeper by asking effective questions such as, “Why does this happen?” This causes layers of branches or “bones” on the diagram. 

6. Identify root causes. 

The final step is to identify the root causes of the effect or problem in the problem statement. To do this, look at the causes that appear most often across multiple categories.

Related terms

• Project plan

• PERT chart

• Gantt chart

• Scope creep

Learn project management with Google

Fishbone diagrams are a valuable tool for identifying the causes and potential causes of any challenges you face. It’s an excellent strategy to consider causes outside of those most obvious to optimise your processes. 

Learn more about tools and resources to aid you in a project management position. Whether you’re just starting your career or looking to upgrade your skills, you can get job-ready at your own pace with the Google Project Management Professional Certificate on Coursera.