How do I conduct a 5 Why investigation?  

How do I conduct a 5 Whys investigation?

The purpose of a 5 Why investigation is to identify the root cause of a problem or nonconformance by repeatedly asking “Why?” to move beyond symptoms and uncover the underlying issue. This ensures that corrective actions address the true cause and prevent recurrence.

Responsibilities

• Investigation Lead: Facilitates the 5 Whys process and documents findings.
• Team Members: Contribute knowledge about the process or system involved.

Steps

Define the Problem

• Clearly describe the issue in factual, measurable terms.
• Avoid assigning blame; focus on what happened, not who is responsible.

Form the Investigation Team

• Involve people who are directly familiar with the process or incident.
• Ensure cross-functional representation if the problem spans multiple areas.

Ask “Why?” (Five Times or As Needed)

• Start with the problem statement and ask “Why did this happen?”
• Record the answer, then ask “Why?” again about that answer.
• Continue this process until you uncover the root cause — the point at which further “Why” questions no longer yield meaningful answers.
• Usually, five iterations are sufficient, but use as many as needed.

Identify Corrective and Preventive Actions

• Develop actions to address the root cause, not just the symptoms.
• Assign responsibility and target completion dates.

Verify Effectiveness

• After corrective actions are implemented, monitor the process to ensure the problem does not recur.
• Document evidence of effectiveness (e.g., audits, performance metrics).

References

• ISO 9001: Root Cause Analysis and Corrective Action
• Lean / Six Sigma Problem Solving Tools
• Internal CAPA or NCR procedures