| No. | Selected time | Intervals number |
| (span >=18) | (18-day) | |
| 1 | 81/04/01~83/01/31 | 654 |
| 2 | 83/07/13~98/05/20 | 5409 |
| A= | 6063 | |
| 1 | 81/04/01~83/01/31 | 654 |
| 2 | 83/07/13~84/06/11 | 318 |
| 3 | 84/06/13~85/04/02 | 277 |
| 4 | 85/04/04~91/07/04 | 2266 |
| 5 | 91/07/06~94/01/16 | 909 |
| 6 | 94/02/07~94/02/24 | 1 |
| 7 | 94/02/26~94/05/24 | 71 |
| 8 | 94/05/26~94/06/14 | 3 |
| 9 | 94/06/16~95/06/25 | 358 |
| 10 | 95/06/27~96/03/19 | 250 |
| 11 | 96/03/21~96/04/30 | 24 |
| 12 | 96/05/02~97/04/25 | 342 |
| 13 | 97/04/28~98/05/20 | 371 |
| B= | 5844 | |
| P=1-B/A= | 3.6% |
Note:
|