Root cause

the cause that, once removed, prevents recurrence

The root cause is the fundamental reason a problem occurred and was not detected. Removing it prevents the problem from coming back. A useful analysis finds both the technical cause (why it occurred) and the system cause (why it escaped).

Methods include 5 Why, the Ishikawa diagram and comparing good and bad parts.

Common mistake

Stopping at a person (“operator error”). Ask why the process allowed the error.

Calculate it

5 Why Analysis: Two 5 Why chains (occurrence and escape), root cause, actions, to 8D.

Related terms

• 5 Why: asking why until the root cause is found
• Ishikawa diagram: fishbone or cause and effect diagram
• Corrective action: removing the cause to prevent recurrence