| Year | Value | | 2024 | 4.499 | | 2023 | 4.59 | | 2022 | 4.593 | | 2021 | 4.597 | | 2020 | 4.6 | | 2019 | 4.603 | | 2018 | 4.607 | | 2017 | 4.61 | | 2016 | 4.613 | | 2015 | 4.617 | | 2014 | 4.62 | | 2013 | 4.623 | | 2012 | 4.633 | | 2011 | 4.63 | | 2010 | 4.81 | | 2009 | 5.004 | | 2008 | 5.113 | | 2007 | 5.261 | | 2006 | 5.412 | | 2005 | 5.563 | | 2004 | 5.712 | | 2003 | 5.839 | | 2002 | 5.971 | | 2001 | 6.143 | | 2000 | 6.317 | | 1999 | 6.489 | | 1998 | 6.639 | | 1997 | 6.82 | | 1996 | 7.004 | | 1995 | 7.525 | | 1994 | 7.795 | | 1993 | 8.048 | | 1992 | 8.272 | | 1991 | 8.459 | | 1990 | 8.606 | | 1989 | 8.713 | | 1988 | 8.786 | | 1987 | 8.833 | | 1986 | 8.858 | | 1985 | 8.864 | | 1984 | 8.853 | | 1983 | 8.828 | | 1982 | 8.793 | | 1981 | 8.752 | | 1980 | 8.71 | | 1979 | 8.671 | | 1978 | 8.501 | | 1977 | 8.466 | | 1976 | 8.423 |
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