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| Fishbone diagram Six Sigma |
Fishbone diagram Six Sigma
The fishbone diagram is the most commonly used cause-and-effect analysis tool in Six Sigma. Cause-and-effect analysis is one of the key tasks in any Six Sigma DMAIC project because half of the game is won when the correct root causes of the problem (the Y) are found.
The team using the fishbone diagram tool should carry out the steps listed below.
- Agree on the problem statement (also referred to as the effect). This is written at the mouth of the “fish.” Be as clear and specific as you can about the problem. Beware of defining the problem in terms of a solution (we need more of something).
- Agree on the major categories of causes of the problem (written as branches from the main arrow). Major categories often include: equipment or supply factors, environmental factors, rules/policy/procedure factors, and people/staff factors.
- Brainstorm all the possible causes of the problem. Ask “Why does this happen?” As each idea is given, the facilitator writes the causal factor as a branch from the appropriate category (places it on the fishbone diagram). Causes can be written in several places if they relate to several categories.
- Again asks “Why does this happen?” about each cause. Write sub-causes branching off the cause branches.
- Continues to ask “Why?” and generate deeper levels of causes and continue organizing them under related causes or categories. This will help you to identify and then address root causes to prevent future problems
Tips:
- Use the fishbone diagram tool to keep the team focused on the causes of the problem, rather than the symptoms.
- Consider drawing your fish on a flip chart or large dry erase board.
- Make sure to leave enough space between the major categories on the diagram so that you can add minor detailed causes later.
- When you are brainstorming causes, consider having team members write each cause on sticky notes, going around the group asking each person for one cause. Continue going through the rounds, getting more causes, until all ideas are exhausted.
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