| Year | Count |
|---|---|
| 1981 | 6 |
| 1982 | 12 |
| 1983 | 5 |
| 1984 | 7 |
| 1986 | 5 |
| 1987 | 10 |
| 1989 | 21 |
| 1990 | 15 |
| 1991 | 5 |
| 1992 | 6 |
| 1993 | 35 |
| 1994 | 35 |
| 1995 | 37 |
| 1996 | 47 |
| 1997 | 92 |
| 1998 | 68 |
| 1999 | 113 |
| 2000 | 163 |
| 2001 | 126 |
| 2002 | 125 |
| 2003 | 123 |
| 2004 | 81 |
| 2005 | 60 |
| 2006 | 61 |
| 2007 | 68 |
| 2008 | 22 |
| 2009 | 34 |
| 2010 | 13 |
| 2011 | 32 |
| 2012 | 15 |
| 2013 | 10 |