| Year | Value | | 2021 | 4.266 | | 2020 | 4.346 | | 2019 | 4.429 | | 2018 | 4.513 | | 2017 | 4.599 | | 2016 | 4.686 | | 2015 | 4.774 | | 2014 | 4.863 | | 2013 | 4.952 | | 2012 | 5.04 | | 2011 | 5.126 | | 2010 | 5.209 | | 2009 | 5.288 | | 2008 | 5.363 | | 2007 | 5.433 | | 2006 | 5.498 | | 2005 | 5.559 | | 2004 | 5.618 | | 2003 | 5.675 | | 2002 | 5.731 | | 2001 | 5.785 | | 2000 | 5.834 | | 1999 | 5.878 | | 1998 | 5.914 | | 1997 | 5.941 | | 1996 | 5.96 | | 1995 | 5.971 | | 1994 | 5.978 | | 1993 | 5.981 | | 1992 | 5.984 | | 1991 | 5.985 | | 1990 | 5.987 | | 1989 | 5.986 | | 1988 | 5.982 | | 1987 | 5.974 | | 1986 | 5.962 | | 1985 | 5.946 | | 1984 | 5.926 | | 1983 | 5.903 | | 1982 | 5.88 | | 1981 | 5.856 | | 1980 | 5.835 | | 1979 | 5.817 | | 1978 | 5.804 | | 1977 | 5.795 | | 1976 | 5.791 | | 1975 | 5.791 | | 1974 | 5.795 | | 1973 | 5.8 | | 1972 | 5.805 | | 1971 | 5.808 | | 1970 | 5.808 | | 1969 | 5.802 | | 1968 | 5.791 | | 1967 | 5.776 | | 1966 | 5.756 | | 1965 | 5.734 | | 1964 | 5.711 | | 1963 | 5.69 | | 1962 | 5.673 | | 1961 | 5.661 | | 1960 | 5.653 |
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