Definition
The final cause of an event or condition; controlling or eliminating it prevents the problem from recurring. Evidence requirement: must be based on direct observation, not reasoning/assumption/deduction.
In detail
Root cause is the deepest cause that leads to a problem, and eliminating it prevents recurrence. It differs from the direct cause (symptom), which is only the surface manifestation, while the root cause is hidden in the system or process. In the problem-solving system, root cause analysis is a core step, identified through direct observation of facts at the gemba, not subjective reasoning. Typically, the output is a clear root cause description that serves as the basis for corrective actions.
Example in practice
When a repetitive quality defect occurs on a production line, the team first lists all possible causes, but through floor observation and data validation, ultimately identifies equipment parameter drift as the root cause. After adjusting parameters and installing poka-yoke devices, the defect no longer occurs. Root cause analysis is used here to avoid fixing only surface issues, ensuring measures are effective and lasting.