| Year | Value | | 2009 | 53.698239878063 | | 2008 | 43.514508307288 | | 2007 | 43.857122318812 | | 2006 | 51.316493089799 | | 2005 | 54.270423940908 | | 2004 | 56.313250115088 | | 2003 | 52.482806315455 | | 2002 | 49.553426885992 | | 2001 | 45.511553305788 | | 2000 | 47.911890587105 | | 1999 | 51.946082241644 | | 1998 | 40.038859204774 | | 1997 | 39.383160450702 | | 1996 | 41.608008759581 | | 1995 | 43.353414125313 | | 1994 | 43.264063059835 | | 1993 | 40.709933637763 | | 1992 | 33.631808975589 | | 1991 | 31.58246613569 | | 1990 | 31.525909490131 |
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