| Year | Count |
|---|---|
| 1968 | 6 |
| 1969 | 7 |
| 1970 | 7 |
| 1971 | 17 |
| 1972 | 13 |
| 1973 | 10 |
| 1974 | 15 |
| 1975 | 13 |
| 1976 | 16 |
| 1977 | 46 |
| 1978 | 42 |
| 1979 | 52 |
| 1980 | 32 |
| 1981 | 20 |
| 1982 | 21 |
| 1983 | 24 |
| 1984 | 25 |
| 1985 | 29 |
| 1986 | 37 |
| 1987 | 47 |
| 1988 | 54 |
| 1989 | 53 |
| 1990 | 70 |
| 1991 | 56 |
| 1992 | 68 |
| 1993 | 46 |
| 1994 | 45 |
| 1995 | 42 |
| 1996 | 49 |
| 1997 | 20 |
| 1998 | 25 |
| 1999 | 16 |
| 2000 | 18 |
| 2001 | 13 |
| 2002 | 14 |
| 2003 | 10 |
| 2004 | 7 |
| 2005 | 11 |
| 2006 | 6 |
| 2007 | 5 |