| Year | Count |
|---|---|
| 1971 | 10 |
| 1972 | 5 |
| 1973 | 5 |
| 1974 | 12 |
| 1975 | 31 |
| 1976 | 35 |
| 1977 | 48 |
| 1978 | 59 |
| 1979 | 79 |
| 1980 | 107 |
| 1981 | 58 |
| 1982 | 53 |
| 1983 | 78 |
| 1984 | 75 |
| 1985 | 136 |
| 1986 | 110 |
| 1987 | 85 |
| 1988 | 129 |
| 1989 | 175 |
| 1990 | 970 |
| 1991 | 1,352 |
| 1992 | 746 |
| 1993 | 569 |
| 1994 | 355 |
| 1995 | 201 |
| 1996 | 117 |
| 1997 | 102 |
| 1998 | 52 |
| 1999 | 7 |