Posted by: JC Gatlin | February 17, 2010

Creating the Fishbone & 5-Why Analysis

The 5 Why Analysis is a question-asking exercise used to explore the cause/effect relationships underlying a particular problem. Ultimately, the goal of applying the 5 Why method is to determine the Root Cause of a defect or problem.

The Fishbone is a diagram that illustrates the thought process behind the 5 Why Analysis.  It shows the Point of Cause in the “head” of the fishbone, the Affinity Statements as the first why of each “rib” or “leg,” and a drill down of WHY? phrases (preferably 5) for each Affinity Statement.

Step 1.
Set-up the Fishbone Diagram by writing the Point of Cause (POC) in the triangular head of the fishbone.

Step 2.
List each Affinity Statement along the body of the fishbone. This statement is your first “why?” so write each Affinity Statement as if answering why it is contributing to the POC. Include a noun and verb in the statement. A single word answer is not acceptable; it will confuse someone reviewing the PDCA.

Step 3.
Now begin the 5 Why Process. For the first Affinity Statement, ask, “why?” at least four more times. Keep your answers as simple as possible, as if you are talking to a child. The Why? answers must be clear, concise phrases that include a noun and a verb. It is critical that the PDCA group drills deep – ask “Why?” at least four more times, if not more.

Step 4.
Sometime, you have two answers to a why question. Show both answers on the fishbone by making a fork that leads the answers into two separate directions. Then continue asking “why?” in both directions.

Although the “five” in 5 Whys is not gospel, it is held that five iterations of asking why is generally sufficient to get to a root cause. Fewer than five and the risk of missing the root cause increases. The real key is to encourage the PDCA group to avoid assumptions and logic traps and instead trace the chain of causality to a root cause that still has some direct connection to the problem statement.

Step 5.
Once you have answered the 5 Whys for each leg of the fishbone, circle the root causes. Do not choose more than 4 root causes within one PDCA. Keep it simple. Also, the root cause will always be an end or final why on the leg. It cannot be a preceding why.

Step 6.
Work the Therefore Test.

Double check that the chain of causality makes sense, and that it’s not missing a Why statement. To do this, begin with the Root Cause (or the final Why) and work backwards saying “therefore” between each answer. This process will often make a missing Why? stick out like a sore thumb.

© February 2010 Homebuilding Partners, Inc.   twitter-logo



  1. […] Creating the Fishbone & 5-Why Analysis dal blog Lean Homebuilding di J.C. Gatlin: Analisi delle 5 perché attraverso il diagramma a lisca di pesce di Ishikawa (traduzione automatica) […]

  2. […] the PDCA form, list the Root Causes from your Fishbone 5-Why Analysis. Every root cause must have at least one counter measure. However, you may have multiple counter […]

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