Fishbone Diagram

Also Called: Cause and Effect Diagram

Fishbone diagrams allow individuals and teams to identify, explore, and display all possible root causes related to a problem or condition. Fishbones allow a team to focus on the content of the problem, rather than the history of the problem, and the causes of the problem rather than the symptoms of the problem.

Types of Fishbone Diagrams

  • Dispersion Analysis: Dispersion analysis uses a fishbone format to categorize types of problems, and continually ask why a problem happens until the team runs out of answers.
  • Process Clarification: Process clarification uses a fishbone to categorize process steps, and continually as why a step occurs until the team runs out of answers.

How to Construct a Fishbone Diagram

1. Problem Statement

Place the problem statement at the head of the "fish." This is the end effect, for which you will start to map out problem causes. Draw a line toward the head of the fish--this is the fish's "backbone."

Fishbone: Problem Statement

2. Categorization

Start listing major steps in the production or service process, and connect them to the backbone in "ribs." There is no specific number of steps or categories you might need to describe the problem, although some common categories are listed below.

Fishbone: Problem Categories

3. Contributing Factors

Brainstorm possible problem causes, and attach each to the appropriate rib.

Fishbone: Contributing Causes

When brainstorming, your team might find it helpful to place ideas on category ribs as they are generated, or to brainstorm an entire list of ideas and then place them on ribs all at once.

Ideally, each contributing factor would fit neatly into a single category, but some causes may seem to fit into multiple categories. If you have a contributing factor that fits into more than one category, place it in each location, and see whether, in the end, considering that factor from multiple points of view has made a difference.

4. Why?

As you list a factor, repeatedly ask your team why that factor is present: Why does staff lack expertise? (Because we don't attend training.)
Why don't we attend training? (Because we don't have the funding.)
Why don't we have the funding? (Because we haven't applied for grants.)
Why don't we apply for grants? (Because we're unaware of sources.)

Sometimes this asking process is called the "Five Whys," as five is often a manageable number to reach a suitable root cause. Your team may need more or less than five whys.

5. Many Ribs: Deeper Causes

You may end up with multiple branches off of each successively smaller rib. Your team might lack expertise, for example, because of a lack of training, but also because you didn't hire the right people for the job. Treat each contributing factor as its own "mini-rib," and keep asking why each factor is occurring.

Continue to push deeper for a clear understanding. While you could likely brainstorm all day, however, it is important to know when to stop to avoid frustration. A good rule of thumb: When a cause is controlled by more than one level of management, remove it from the group.

6. Test for Root Causes

Test for root causes by looking for causes that appear repeatedly within categories or across major categories.

(Hint: Use check sheets to determine the frequencies of various causes, and scatter plots to test the strength of cause-effect correlation.)

Further Reading

More Information

Icon MDH: Root Cause Analysis Toolkit
Icon American Society for Quality (ASQ): Fishbone Diagram
Icon Improhealth Collaborative: Fishbone Diagram (PDF: 337KB / 7 pages)

Examples of Fishbone Diagrams

Icon AIDS Training and Education Centers: Using a Fishbone Diagram to Assess and Remedy Barriers to Cervical Cancer Screening in Your Healthcare Setting
Icon West Central Public Health Initiative: Immunization Quality Improvement Project (PDF, p.4: 428KB / 10 pages)


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