What are fishbone diagrams?

Fishbone diagrams are a Lean problem-solving tool used to identify the root cause of an issue. The goal is to reveal relationships between variables Performing a root cause analysis is one of Lean’s most important methods for problem solving and implementing corrective actions that will prevent the problem from happening again.

You may also see these charts referred to as Ishikawa diagrams, named after Kaoru Ishikawa, a pioneer for modern management processes, who popularized this visual brainstorming method in the 1960s. It is now however commonly known as a fishbone diagram because your completed analysis will look like a fish skeleton. Fishbone diagrams are causal diagrams that captures all possible causes and keeps attention focused on the issue at hand. These cause-and-effect diagrams are most effective when utilized in group settings and can serve as a framework for brainstorming sessions.

Teams looking to utilize the fishbone diagram in root cause analysis should consider the following steps:

  • Write a problem statement: A problem statement (aka the effect) is defined. Be clear and specific, what exactly is the problem you are trying to solve? This will be recorded in the “head” of the fish.
  • Come up with categories: From there, the “backbone” of the fish will run across the page with “ribs” branching out. Each “rib” represents a major category of causes to the problem. Some examples of major categories include methods, machines, environmental factors, etc.
  • Ask why: Begin brainstorming possible causes and as a team work through the Five Whys, asking “Why?” about each cause. Sub-causes are branched off the ribs and written in the appropriate category.
  • Ask again: It’s critical to keep asking Why until all idea are exhausted. Generate deeper levels of causes and keep digging until you have truly reached the root cause of a problem, this will be the starting point for your next continuous improvement project.

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