| Year | Very high | High | Moderate |
|---|---|---|---|
| 1980 | 12 | 18 | 69 |
| 1981 | 22 | 20 | 43 |
| 1982 | 10 | 17 | 65 |
| 1983 | 13 | 12 | 67 |
| 1984 | 6 | 13 | 40 |
| 1985 | 9 | 5 | 21 |
| 1986 | 4 | 11 | 29 |
| 1987 | 20 | 12 | 46 |
| 1988 | 17 | 20 | 34 |
| 1989 | 12 | 11 | 28 |
| 1990 | 23 | 17 | 22 |
| 1991 | 20 | 18 | 34 |
| 1992 | 25 | 28 | 35 |
| 1993 | 26 | 21 | 45 |
| 1994 | 42 | 14 | 31 |
| 1995 | 35 | 25 | 54 |
| 1996 | 19 | 19 | 52 |
| 1997 | 31 | 27 | 97 |
| 1998 | 44 | 20 | 32 |
| 1999 | 33 | 30 | 68 |
| 2000 | 38 | 41 | 49 |
| 2001 | 34 | 21 | 135 |
| 2002 | 77 | 32 | 64 |
| 2003 | 28 | 37 | 99 |
| 2004 | 23 | 35 | 73 |
| 2005 | 54 | 23 | 66 |
| 2006 | 42 | 37 | 120 |
| 2007 | 47 | 31 | 83 |
| 2008 | 29 | 27 | 64 |
| 2009 | 23 | 40 | 77 |
| 2010 | 71 | 46 | 204 |