| Year | Value | | 2021 | 4.644 | | 2020 | 4.713 | | 2019 | 4.783 | | 2018 | 4.852 | | 2017 | 4.922 | | 2016 | 4.992 | | 2015 | 5.062 | | 2014 | 5.131 | | 2013 | 5.34 | | 2012 | 5.451 | | 2011 | 5.551 | | 2010 | 5.63 | | 2009 | 5.626 | | 2008 | 5.579 | | 2007 | 5.513 | | 2006 | 5.55 | | 2005 | 5.609 | | 2004 | 5.667 | | 2003 | 5.733 | | 2002 | 5.734 | | 2001 | 5.778 | | 2000 | 5.812 | | 1999 | 5.833 | | 1998 | 5.86 | | 1997 | 5.885 | | 1996 | 5.85 | | 1995 | 5.895 | | 1994 | 5.958 | | 1993 | 6.025 | | 1992 | 6.099 | | 1991 | 6.159 | | 1990 | 6.221 | | 1989 | 6.275 | | 1988 | 6.304 | | 1987 | 6.34 | | 1986 | 6.364 | | 1985 | 6.377 | | 1984 | 6.401 | | 1983 | 6.391 | | 1982 | 6.403 | | 1981 | 6.457 | | 1980 | 6.515 | | 1979 | 6.577 | | 1978 | 6.61 | | 1977 | 6.643 | | 1976 | 6.664 | | 1975 | 6.693 | | 1974 | 6.712 | | 1973 | 6.73 | | 1972 | 6.739 | | 1971 | 6.721 | | 1970 | 6.717 | | 1969 | 6.708 | | 1968 | 6.668 | | 1967 | 6.625 | | 1966 | 6.592 | | 1965 | 6.546 | | 1964 | 6.517 | | 1963 | 6.492 | | 1962 | 6.446 | | 1961 | 6.379 | | 1960 | 6.315 |
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