Editor’s note: This article was originally published July 14, 2006.

Problems arise on many projects. A proactive project manager should have a set of problem resolution techniques that can be applied in different instances. One technique for analyzing complex problems that appear to have many interrelated causes is called a “cause and effect” diagram. Because of its shape, this technique is also called a Fishbone Diagram. (Another name you might hear for this technique is an Ishikawa Diagram. This is named for Professor Kaoru Ishikawa, a Japanese professor who pioneered the diagram in 1943.) Some benefits of a Fishbone Diagram include:

  • It allows various categories of causes to be explored.
  • It encourages creativity through a brainstorming process.
  • It provides a visual image of the problem and potential categories of causes.

The following description and examples show how the problem-solving technique works.

First, describe the problem on the far right side of the diagram. This may be the actual problem or it may be a symptom — at this point you’re not exactly sure.

Draw a long horizontal arrow pointing to the box. This arrow will serve as the backbone from which further major and minor causes will be categorized and related. (See Figure A.)
Figure A

Identify potential causes and group them into major categories along the “bones” of the Fishbone Diagram. You should brainstorm to identify the major categories; at this point, you shouldn’t be concerned if there’s disagreement about whether a category holds the potential cause — just put them all up. Make sure to leave enough space between the major categories on the diagram so that you can add minor detailed causes in later. (See Figure B.)
Figure B

Continue to brainstorm the causes by looking at more detailed explanations for each of the major cause categories identified above. The team should ask whether each category is a cause, or if it is a symptom. If it’s a symptom, try to identify the more detailed causes on slanted lines that hook up to the appropriate major category lines. (See Figure C.)
Figure C

Sometimes, the detailed causes will have other, more granular causes coming off of them. If so, connect additional lines to the detailed lines. Three levels of detail is usually the practical limit for this diagram.

When you finish brainstorming major causes/symptoms and more detailed causes and symptoms, the team can begin analyzing the information. Evaluate each major cause and the potential detailed causes associated with it. Remember that the original list was compiled by brainstorming where all ideas are included. Now, you must determine which items seem more likely to be the cause (or one of the causes). Circle the items that are most likely and need to be investigated further.

If there’s not an obvious consensus on the top areas to investigate, use some sort of voting system to formally narrow down the top choices with the biggest chance of success. For each item circled, discuss how the item impacts the problem.

Once you circle the causes that appear to be the most likely, you should create an action plan for attaching these causes. This will most likely involve some high-level actions and assigning the cause to a team member to be analyzed outside of the meeting.

Remember that this technique is used for complex problems with multiple causes and allows you to identify potential causes for the problem and determine which ones are most likely to be resolved.