Probability of failure. The probability that the tree or selected tree part will fail within a year.
| Probability of failure range | Probability of failure percentage | Probability ratio |
|---|---|---|
| 1 Very high | 51–100 | 1/1 |
| 2 High | 11–50 | 1/2 |
| 3 Moderate | 1–10 | 1/10 |
| 4 Low | 0.1–0.9 | 1/100 |
| 5 Very low | < 0.1 | 1/1,000 |