Year | Value | 2020 | 7.06 | 2019 | 7 | 2018 | 6.92 | 2017 | 6.85 | 2016 | 6.81 | 2015 | 6.76 | 2014 | 6.68 | 2013 | 6.65 | 2012 | 6.57 | 2011 | 6.48 | 2010 | 6.63 | 2009 | 6.95 | 2008 | 6.86 | 2007 | 6.79 | 2006 | 6.96 | 2005 | 6.95 | 2004 | 6.86 | 2003 | 6.83 | 2002 | 7.72 | 2001 | 7.95 | 2000 | 7.88 | 1999 | 7.3099999428 | 1998 | 7.3099999428 | 1997 | 7.3800001144 | 1996 | 7.5599999428 | 1995 | 7.6399998665 | 1994 | 7.6944999695 | 1993 | 7.8699002266 | 1992 | 7.8621001244 | 1991 | 8.9221000671 | 1990 | 8.9198999405 | 1989 | 8.9371004104614 | 1988 | 8.9421997070312 | 1987 | 8.9502000808716 | 1986 | 8.9465999603272 | 1985 | 8.9404001235962 | 1984 | 8.8957996368408 | 1982 | 8.8107004165649 | 1981 | 8.7750997543335 | 1980 | 8.7762002944946 |
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