Multiplication hides things. A row with severity 9, occurrence 2, and detection 3 has an RPN of 54, which would sit far down most lists. A row with severity 3, occurrence 7, and detection 5 has an RPN of 105 and would sit above it. Sorting by RPN alone would have you fixing a cosmetic problem before a rare event that could seriously harm a patient.
Most experienced teams apply a second rule: any row with a severity of 9 or 10 gets reviewed and acted on regardless of its RPN. Some also look at severity times occurrence as a pair, sometimes called criticality, because a severe effect that also happens often is the worst combination even if detection is good today. Detection controls can fail; severity does not go away.
A sensible review order is: first, all rows with severity 9 or 10; second, rows with high severity and high occurrence; third, the remaining rows sorted by RPN. This keeps the arithmetic useful while making sure the number does not bury a hazard.
Standard Procedure
- 1Flag every row with a severity score of 9 or 10 before looking at RPN.
- 2Flag rows where severity and occurrence are both 7 or more.
- 3Rank the remaining rows by RPN.
- 4Document the review order so an auditor or new team member can see why a low-RPN row was prioritized.
Lesson Summary
- ✓A low RPN can hide a severe effect behind low occurrence and good detection.
- ✓Review by severity first, then severity and occurrence together, then RPN.