Fishbone diagrams are useful for documenting team input related to possible causes, but when relied upon too heavily can result in failed efforts to understand and control variation.
As long as team members understand that fishbone diagrams are only useful for organizing possible causes, they will be okay. But here is where many projects go off track and fail:
The team selects one or two potential causes (often by consensus or voting) from the fishbone diagram and, without further analysis, dedicates an enormous effort toward fixing those potential causes. More often than not, the team’s consensus vote is wrong, the project fails, and the project leader loses credibility in the organization.
Here is a great example of a team in a hospital environment that created a very impressive looking fishbone diagram, but what does a team do with over forty potential causes? Very little. A better approach would have been to conduct a root cause analysis of each incident, and then organize the causes into a Pareto chart.
With all of that said, fishbone diagrams are useful for gathering team input early in a project, but the value begins and ends there. Here are some guidelines for completing a fishbone diagram.
Completing a Fishbone Diagram
(see the Downloads tab if you need a template)
Plan the Meeting
- Fishbone diagrams are best completed in a team setting, where those most knowledgable about the problem-at-hand get together and combine their thoughts to complete the diagram.
- Plan the meeting at least one week in advance, and clearly communicate the meeting objective.
- An example of a meeting objective might be: ”Complete a fishbone diagram for motor life cycle failures we are experiencing, and use this information as an input to our root cause analysis plan.”
- At the start of the meeting, show a fishbone diagram example, review the meeting objective, and ask for any questions on the definition/scope of the problem to be discussed.
- If you are solving a manufacturing problem, it is helpful to review the “6 M’s” that the potential causes will likely fall into Manpower, Methods, Machines, Metrics, Materials, and Minutes (time).
- Go around the room and ask team members what they think the potential contributors of the problem could be, write the ideas on small pieces of paper (sticky notes are ideal), and stick them on the wall or large dry-erase board.
- Keep the meeting moving and avoid discussing any one cause for too long.
- Once all of the potential causes have been listed, group the them under major headings like the 6 M’s above. It’s okay not to have the headings decided upon at the start of the meeting. Sometimes it’s best to identify the group headings once the potential causes are listed.
- Each group heading will represent a bone on the fish (reference the introduction page), and then the individual causes can be listed along each bone.
For more fishbone diagram examples and templates, see fishbonediagram.org.
Here is a fishbone diagram for a quality issue in a power tool assembly plant.
Specifically, a cordless drill line was failing in the field (high warranty rate) due to drills “clutch-out in drill mode,” i.e. the drill clutch was slipping when holes were being drilled (clutching is only supposed to take place when driving screws).
In the above case, the team grouped possible causes into the three categories noted on the diagram (Assembly, Design, Purchased Components). Note that numbers in red font represent the causes that the team will investigate first, not address first.