| Years since operation | Start number | Fail number | Died | Lost | Revised but not loose | Number at risk at end of period | Survival rate% | 95% CI |
| 0 to 1 | 228 | 2 | 5 | 0 | 4 | 223.5 | 99.1 | 100 to 100 |
| 1 to 2 | 217 | 0 | 8 | 0 | 2 | 212 | 99.1 | 99.1 to 99.1 |
| 2 to 3 | 207 | 0 | 5 | 2 | 1 | 203 | 99.1 | 99.1 to 99.1 |
| 3 to 4 | 199 | 0 | 7 | 0 | 0 | 195.5 | 99.1 | 99.1 to 99.1 |
| 4 to 5 | 192 | 2 | 5 | 1 | 1 | 188.5 | 98 | 99.1 to 99.1 |
| 5 to 6 | 183 | 0 | 8 | 0 | 0 | 179 | 98 | 96.1 to 99.9 |
| 6 to 7 | 175 | 0 | 9 | 3 | 0 | 169 | 98 | 96.1 to 99.9 |
| 7 to 8 | 163 | 1 | 14 | 1 | 1 | 155 | 97.4 | 96.1 to 99.9 |
| 8 to 9 | 146 | 1 | 6 | 0 | 0 | 136 | 96.7 | 94.7 to 100 |
| 9 to 10 | 125 | 0 | 3 | 0 | 0 | 113.5 | 96.7 | 93.5 to 100 |
| 10 to 11 | 102 | 3 | 5 | 0 | 0 | 85.5 | 93.2 | 92.9 to 100 |
| 11 to 12 | 66 | 1 | 2 | 2 | 0 | 59 | 91.5 | 87.3 to 99.4 |
| 12 to 13 | 51 | 0 | 1 | 1 | 0 | 44.5 | 91.5 | 83.9 to 99.6 |
| 13 to 14 | 38 | 0 | 3 | 0 | 0 | 28 | 91.5 | 82.1 to 100 |
| 14 to 15 | 18 | 0 | 4 | 0 | 0 | 13.5 | 91.5 | 77.7 to 100 |
| 15 to 16 | 9 | 0 | 1 | 0 | 0 | 7.5 | 91.5 | 72.9 to 100 |
| 16 to 17 | 6 | 0 | 1 | 0 | 0 | 5 | 91.5 | 68.7 to 100 |
| 17 to 18 | 4 | 0 | 0 | 0 | 0 | 3.5 | 91.5 | 64.2 to 100 |
| 18 to 19 | 3 | 0 | 0 | 0 | 0 | 1.5 | 91.5 | 49.6 to 100 |