| Year | Value | | 2014 | 1.708 | | 2013 | 1.693 | | 2012 | 1.709 | | 2011 | 1.702 | | 2010 | 1.677 | | 2009 | 1.621 | | 2008 | 1.899 | | 2007 | 1.863 | | 2006 | 1.88 | | 2005 | 1.915 | | 2004 | 1.911 | | 2003 | 1.902 | | 2002 | 2.005 | | 2001 | 2.094 | | 2000 | 2.152 | | 1999 | 2.095 | | 1998 | 2.039 | | 1997 | 1.925 | | 1996 | 1.982 | | 1995 | 2.046 | | 1994 | 2.178 | | 1993 | 2.122 | | 1992 | 2.311 | | 1991 | 2.549 | | 1990 | 2.497 | | 1987 | 2.582 | | 1986 | 2.556 | | 1985 | 2.527 |
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