One of the most often used cause-and-effect diagrams is a Fishbone Diagram. It appears very simple but the results are outstanding. As a result, it is used very often and one that should be mastered. Why would you use it?
- Allows various categories of causes to be explored.
- Encourages creativity through a brainstorming process.
- Provides a visual image of the problem and potential categories of causes
- Analyze Complex problems that seem to have many interrelated causes
To create a Fishbone Diagram:
1. 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 are not exactly sure.
2. 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.
3. Identify potential causes and group them into major categories. Examples of major categories include people, processes, material, equipment, environment, etc. The major categories are identified using brainstorming techniques, so at this point you are not worried if there is disagreement about whether a category holds the potential cause or not. 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. Each of these major categories will be explored in more detail.
4. Continue to brainstorm the causes by looking at more detailed explanations for each of the major cause categories identified above. Write the more detailed causes on slanted lines that hook up to the appropriate major category lines.
5. 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.
6. When you are done brainstorming major categories and more detailed potential causes, begin analyzing the information you have compiled. 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 like they are more likely to be the cause (or one of the causes). Circle the items that are most promising and should be investigated further.
7. If there is 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 most chance of success.
8. For each item circled, discuss how the item impacts the problem.
9. Create an action plan for resolving the circled causes. Remember that there may be a number of potential causes that interact together to create the problem. The action plan must account for these inter-dependencies. If the detailed causes are still complex, or if not enough information is known, they may be assigned to one or more people for further analysis outside of the meeting.
P.S. The fish can swim either way, right or left!
Source of information: Ten Step Project Management archive of Newsletters.
The Fishbone is an integral part of the Measure phase of the DMAIC Six Sigma Process