Root Cause Analysis

Use a Fishbone Diagram to Find the Root Causes

When I first started conducting root cause analysis sessions 25 years ago, everyone wondered: "Why is the head of the fishbone on the right, not the left?" I began to say: "It's because the effect is the result of the things that came before it." Since most people organize time from left to right, that made sense for most people.

Purpose of the Fishbone or Ishikawa Diagram

The real purpose of the fishbone diagram is to get people talking about the causes and to organize them visually so that a team can discuss them and decide what to fix. I invariably start by asking the Five Whys and diagramming the cause-effects using Post-it® Notes. Using Post-its allows the team to move causes around and reorganize the cause-effects as the problem becomes clearer. Sometimes a "Why?" belongs somewhere else. Sometimes the cause-effect logic breaks down and we need to add a different cause.


I have found that a properly focused improvement team can find root causes easily. The only tarpit is whalebone diagramming when the project is too broad. One of my early projects had a fishbone that covered every wall of a conference room. We had to go back and narrow our focus.

Once the team has figured out the Five Whys, diagrammed the fishbone, checked the logic and identified the root causes, it's easy to create a fishbone diagram in excel using QI Macros automated Ishikawa/Fishbone template.


The next step is to figure out what countermeasures will prevent the root causes. I often find that the team can't stop themselves from offering "solutions" as we go through the root cause analysis, so I capture them on a separate flipchart as we ask the Five Whys. This 1) honors the suggestion and 2) creates a starting point for developing countermeasures. Often, however, "solutions" offered early in the root cause analysis are not valid when the team identifies the real root cause.

Master the Ishikawa/Fishbone Diagram and you'll be well on your way to creating breakthrough improvement with Six Sigma. QI Macros will support you every step of the way.

To learn more about Breakthrough Improvement with the QI Macros and Excel, get my new book (click here) and watch the supporting videos (click here).

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