What Is a Fishbone (Ishikawa) Diagram?

Problems can occur in manufacturing. Some problems are larger than others. Some reoccur, and others arise only once. Regardless of frequency, is important to understand what causes these problems so they can be eliminated.

A fishbone diagram (also known as an Ishikawa diagram) can be a useful tool to identify, manage, and eliminate the root cause of problems. The diagram in its simplest form is designed to look like the skeleton of a fish—hence the name. Kaoru Ishikawa is credited with creating the fishbone diagram to help solve his company’s operational problems in 1968.

Before exploring how to create a fishbone diagram, let’s review some key terminology and basics of problem-solving:

• Problem: An unwelcome situation or outcome that needs to be dealt with to achieve the desired positive result.
• Effect: A result of an action or cause.
• Cause: An input that generates an action, condition, or phenomenon.
• Root Cause: The trigger for the cause.

Problem-Solving and Root Cause

Humans are good at identifying problems and their cause. However, when problems recur, it can be difficult to determine why addressing the cause did not fix the problem for good. This is often because the root cause has not been addressed. 

For instance, consider that a bread manufacturer encounters an issue with dough not rising. The problem is that the dough did not rise to the desired height. The cause could have been that the yeast did not have enough sugar to generate the right amount of CO2. The effect was that without enough CO2 the dough could not rise to the desired shape or size.

But what is the root cause for why insufficient sugar was added to the dough? Was it faulty equipment? A bad recipe? Human error? Solving the root cause is necessary in order to prevent the problem from reoccurring. 

An important part in identifying a root cause is assembling a cross-functional team. You should consider not only having engineers or subject matter experts (SMEs) in the group, but also line operators, people upstream and downstream from the problem, and in certain cases customers and suppliers.

Explore the benefits of using a fishbone diagram in the next article.