By Theresa Heitman, Consultant and Trainer for IQC
The Fishbone Diagram or Cause and Effect Diagram is one of the most powerful tools you can use for identifying possible causes to a problem. It is called a Fishbone Diagram because it looks like the skeleton of a fish.
The structure of this tool helps a problem-solving team systematically think through and organize all the elements that could be contributing to the problem or the effect.
Although this tool can seem a little complex at first, once you have practiced using the Fishbone Diagram and discover how it uncovers possible causes and helps lead you to creating an action plan for eliminating or reducing the problem, it will become one of your favorite “go to” problem solving tools.
To construct this diagram:
1. Draw a horizontal straight line. This is the spine of the fish.
2. Draw a box on the right end of the line. This is the head of the fish. Write the problem or the effect in this box.
3. Draw five angled lines (bones) coming off the horizontal line. These are the bones of the fish. Your diagram should look similar to the drawing below.
4. Label each bone of the fish with a category. Typically, causes of problems are found in the following categories: Environment, Methods, Machines, People, and Materials. These labels are only suggested. The team may name their own categories if desired.
Now it is time to ask the questions. Pick one category and ask, “What about ‘Methods’ is causing the problem/effect?” Draw a line and label it for each cause in that category. As you work systematically through the main categories you will likely identify many causes contributing to the problem. You can further drill down on the causes by adding more “fish” bones. Sometimes the preferred method of identifying causes is brainstorming. When you record one cause per sticky note, you can easily stick the causes on to the category where it occurs.
You may notice that one or two categories tend to have the majority of the causes, which may help you see where it might be best to concentrate your effort.
Next, the team will need to select 5-7 of the most likely causes. Further root cause analysis is performed from here. A data collection plan may be needed to understand the variation and identify the root cause. An interrelationship Digraph is often helpful to identify the causes that are the main drivers.
- Remember that this stage in the problem-solving process focuses on causes, NOT potential solutions.
- The most important step is phrasing the problem/effect. Make sure you understand what the problem really is.
IQC Members can download a template for a fishbone diagram here.