Fishbone (Ishikawa) diagram

The fishbone diagram is for sorting ideas into categories and it can be used for structuring a brainstorming session. This cause analysis tool is considered one of the seven basic quality tools. The fishbone diagram identifies many possible causes for an effect or problem.

Format MethodTimeframe 1 - 2 hoursGroup Size AllFacilitation Level MediumRequired Materials Pen and paper, Post its


  • Agree on a problem statement (effect). Write it at the center right of the flipchart or whiteboard. Draw a box around it and draw a horizontal arrow running to it.
  • Brainstorm the major categories of causes of the problem. If this is difficult use generic headings.
  • Write the categories of causes as branches from the main arrow.
  • Brainstorm all the possible causes of the problem. Ask "Why does this happen?" As each idea is given, the facilitator writes it as a branch from the appropriate category. Causes can be written in several places if they relate to several categories.
  • Again ask "Why does this happen?" about each cause. Write sub-causes branching off the causes. Continue to ask "Why?" and generate deeper levels of causes. Layers of branches indicate causal relationships.
  • When the group runs out of ideas, focus attention to places on the chart where ideas are few.


The Fishbone diagram can be used to structure a brainstorming session. It immediately sorts ideas into useful categories.


Follow the process step by step – do not rush into a presumed root cause. Make a clear division of the causes of problems and the symptoms of the problem. Focus on long-term solutions/