I recently came across a good post about fishbone diagrams on Christian Paulsen's Lean Leadership blog.
Fishbones (also called cause-and-effect, C&E or Ishikawa diagrams) help you brainstorm potential causes of a problem--and see relationships among potential causes.
Brainstorming frequently gets a bad rap. Some people have had bad experiences with brainstorming sessions that were too loose, and consequently didn't result in any useful information or ideas. But when its done in a structured way it's a very useful tool, and can reveal potential causes that wouldn't be immediately obvious.
These diagrams give you a great way to brainstorm within a well-defined structure. You place a central problem, or effect, on the far right of the diagram, then branch "affinities" or types of causes from the spine of the central effect. The specific causes then branch from the affinities.
Paulsen points to the effectiveness of this tool for root cause analysis, or as a way to explore several potential causes of problems, focusing on one particular type of diagram.
It's worth mentioning that Lean Six Sigma tools frequently come in different "flavors,", some of which may be better suited to your particular project or challenge. For instance, some Ishikawa diagrams are better for manufacturing than for other types of businesses.
I'm aware of at least five different types, each suited to a different challenge or approach.
In its basic form, the cause-and-effect diagram has no predetermined affinities, or categories of causes, so you can determine affinities that may be unique to your organization. For example, a public relations firm may have affinities that wouldn't be found in a manufacturing operation, and vice versa.
This type of C&E diagram is commonly used in the service industry. It organizes information about potential causes into four common categories: Suppliers, Systems, Surroundings, and Skills.
This type uses 8 categories: Procedures, Policies, Place, Product, People, Processes, Price, and Promotion. This variation is also commonly used in the service industry, but can certainly be applied in nearly any type of business.
Man Machines Materials Fishbone
This variation, commonly used in manufacturing, allows you to organize potential causes of a problem into these categories: Man, Materials, Machine, Methods, Measurements, and Environment. In some cases, two additional categories are included: Management/Money and Maintenance.
These four Fishbone templates are built into Minitab's Companion software for executing and reporting on quality improvement, along with dozens of other Lean Six Sigma forms and tools. You can use other tools, of course, or just draw out your fishbone diagram on paper. But a cool thing about doing a fishbone diagram in Companion is that the factors you enter during your brainstorming session can be drag-and-dropped and/or autofilled into other tools, reducing the need to re-enter data.
Design of Experiments Fishbone
A last type of Fishbone diagram allows structured brainstorming about potential factors for a response variable to help you design an experiment. You can use this diagram to organize information about potential factors of response variables into Controllable, Uncontrollable, Held-Constant, and Blockable Nuisance categories.