| 1996 | 1997 | 1998 | 1999 | 2000 | |
| JAN | 14.1 | 12.1 | 12.6 | 15.2 | |
| FEB | 15.4 | 14.2 | 16.1 | ||
| MAR | 21.8 | 10.7 | 17.1 | 18.9 | |
| APR | 22.5 | 17.2 | 21.9 | 30.3 | |
| MAY | 33.7 | 31.4 | 28.7 | 26.3 | 35.4 |
| JUN | 34.0 | 32.3 | 36.9 | 33.6 | 35.1 |
| JUL | 32.3 | 35.8 | 35.6 | 34.7 | 31.9 |
| AUG | 29.8 | 25.9 | 26.2 | 28.4 | 28.5 |
| SEP | 23.9 | 25.5 | 25.2 | 25.9 | 28.2 |
| OCT | 23.1 | 23.3 | 21.6 | 24.1 | |
| NOV | 16.6 | 15.0 | 18.2 | 11.2 | |
| DEC | 14.4 | 14.1 | 11.8 | 10.3 |