| Year | Count |
|---|---|
| 1981 | 6 |
| 1983 | 5 |
| 1986 | 6 |
| 1987 | 5 |
| 1988 | 6 |
| 1989 | 8 |
| 1990 | 7 |
| 1991 | 11 |
| 1992 | 11 |
| 1993 | 10 |
| 1994 | 13 |
| 1995 | 15 |
| 1996 | 24 |
| 1997 | 20 |
| 1998 | 33 |
| 1999 | 16 |
| 2000 | 22 |
| 2001 | 16 |
| 2002 | 22 |
| 2003 | 27 |
| 2004 | 14 |
| 2005 | 15 |
| 2006 | 9 |
| 2007 | 14 |
| 2008 | 14 |
| 2009 | 17 |
| 2010 | 10 |
| 2011 | 9 |
| 2012 | 5 |
| 2013 | 7 |
| 2014 | 6 |
| 2015 | 10 |