| Year | Value | | 2014 | 4.67 | | 2013 | 4.76 | | 2012 | 4.83 | | 2011 | 4.95 | | 2010 | 5.08 | | 2009 | 5.19 | | 2008 | 5.3 | | 2007 | 5.44 | | 2006 | 6.12 | | 2005 | 5.87 | | 2004 | 6.04 | | 2003 | 6.12 | | 2002 | 6.27 | | 2001 | 6.4 | | 2000 | 6.54 | | 1999 | 6.8000001907 | | 1998 | 6.9099998474 | | 1997 | 7.2199997902 | | 1996 | 7.4699997902 | | 1995 | 8.1999998093 | | 1994 | 8.9413003922 | | 1993 | 10.6812000275 | | 1992 | 11.2423000336 | | 1991 | 10.9629001617 | | 1990 | 10.6618003845 | | 1989 | 10.629799842834 | | 1988 | 10.674200057983 | | 1987 | 10.655599594116 | | 1986 | 10.64490032196 | | 1985 | 10.644800186157 |
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