| Year | Value | | 2009 | 46.193551602144 | | 2008 | 30.343152296218 | | 2007 | 29.1842777711 | | 2006 | 29.540884301319 | | 2005 | 33.927115132276 | | 2004 | 27.273042612919 | | 2003 | 30.352377056541 | | 2002 | 33.59083783313 | | 2001 | 31.230870340813 | | 2000 | 40.864409985227 | | 1999 | 40.126298421858 | | 1998 | 40.986735965476 | | 1997 | 39.670387725631 | | 1996 | 43.03527636295 | | 1995 | 47.352058090756 | | 1994 | 44.211700244866 | | 1993 | 45.551561128882 | | 1992 | 41.615463814806 | | 1991 | 35.573469550642 | | 1990 | 30.782337763497 |
|