The quantitative frequency ranges use orders-of-magnitude boundaries aligned with ISO 14971:2019 Annex D guidance on probability estimation. Each level represents a tenfold increase in occurrence frequency.
P1 Probability Scale
| Level | ID | Name | Frequency Range | Description |
|---|---|---|---|---|
| 0 | 0 | Unanalyzed | — | Default. Item has not yet been assessed. |
| 1 | 1 | Very unlikely | ≤ 1 / 100,000 | Injury would be extremely rare over the device lifetime |
| 2 | 2 | Unlikely | ≤ 1 / 10,000 | Injury would be rare; isolated occurrence possible |
| 3 | 3 | Possible | ≤ 1 / 1,000 | Hazardous situation may occur during routine use |
| 4 | 4 | Likely | ≤ 1 / 100 | Hazardous situation expected to occur periodically |
| 5 | 5 | Very likely | ≤ 1 / 1 | Hazardous situation expected to occur frequently or continuously |
Fields Using This Enumeration
ThepOccurrence enum is used on two Risk Record fields, representing the before/after states of risk control:
| Field | ID | Stage |
|---|---|---|
| Pre-mitigation P1 | preHazardProbability | Initial risk evaluation — before any risk controls |
| Post-mitigation P1 | postHazardProbability | Residual risk evaluation — after risk controls are applied |
Role in the Two-Factor Probability Model
The Medical Device Safety Solution decomposes overall probability into two independent factors, following ISO 14971 guidance:
| P1 x P2 Product | Composite Probability (P) |
|---|---|
| 1 — 3 | 1 (Very low) |
| 4 — 8 | 2 (Low) |
| 9 — 13 | 3 (Moderate) |
| 14 — 18 | 4 (High) |
| 19 — 25 | 5 (Very high) |
The HARA risksheet uses threshold-based bucketing (boundaries at 3, 8, 13, 18), while the DFMEA risksheet uses linear bucketing via
Math.ceil(product / 5). The two algorithms produce slightly different results at certain boundary values.P1 x P2 Quick Reference Matrix
This matrix shows the composite probability P for each P1/P2 combination using the HARA bucketing algorithm:| P2=1 | P2=2 | P2=3 | P2=4 | P2=5 | |
|---|---|---|---|---|---|
| P1=1 | 1 | 1 | 1 | 2 | 2 |
| P1=2 | 1 | 2 | 2 | 2 | 3 |
| P1=3 | 1 | 2 | 3 | 3 | 3 |
| P1=4 | 2 | 2 | 3 | 4 | 4 |
| P1=5 | 2 | 3 | 3 | 4 | 5 |
Configuration Details
| Property | Value |
|---|---|
| Source file | .polarion/tracker/fields/pOccurrence-enum.xml |
| Enum type | pOccurrence |
| Applied to | Risk Record (preHazardProbability, postHazardProbability) |
| Risksheet columns | pHazardBefore, pHazardAfter |
| Combined via | riskProbabilityPre / riskProbabilityPost formulas |
| Used in reports | Risk Matrix Report, ISO 14971 HARA Report (Section 2 scales) |
Related Pages
- P2 Harm Probability Levels — the second factor in the probability model
- Risk Classification — the three outcomes derived from the risk matrix
- Risk Matrix and P1xP2 Probability Model — conceptual explanation of the dual-probability approach
- Evaluate Initial Risk (Pre-Mitigation) — how to assign P1 and P2 values
- HARA Risksheet Configuration Reference — column definitions for probability fields
Sources
Sources
Code:
pOccurrence-enum.xml, riskRecord-custom-fields.xml, risksheetTopPanel.vm (HARA), iso-14971-hara-report page.xml