| Length of time | Proportion of beta unstable | |
| Significant level 5% | Significant level 10% | |
| 6 months | 15.21% | 22.47% |
| 12 months | 17.21% | 24.71% |
| 18 months | 25.32% | 33.65% |
| 24 months | 23.08% | 28.61% |
| 36 months | 22.60% | 30.29% |