| Year | Value | | 2021 | 3.018 | | 2020 | 3.049 | | 2019 | 3.094 | | 2018 | 3.139 | | 2017 | 3.187 | | 2016 | 3.239 | | 2015 | 3.264 | | 2014 | 3.288 | | 2013 | 3.334 | | 2012 | 3.305 | | 2011 | 3.318 | | 2010 | 3.249 | | 2009 | 3.318 | | 2008 | 3.408 | | 2007 | 3.441 | | 2006 | 3.43 | | 2005 | 3.438 | | 2004 | 3.519 | | 2003 | 3.635 | | 2002 | 3.677 | | 2001 | 3.657 | | 2000 | 3.658 | | 1999 | 3.736 | | 1998 | 3.855 | | 1997 | 3.993 | | 1996 | 4.071 | | 1995 | 4.143 | | 1994 | 4.217 | | 1993 | 4.366 | | 1992 | 4.522 | | 1991 | 4.645 | | 1990 | 4.759 | | 1989 | 4.904 | | 1988 | 5.046 | | 1987 | 5.161 | | 1986 | 5.276 | | 1985 | 5.373 | | 1984 | 5.463 | | 1983 | 5.542 | | 1982 | 5.613 | | 1981 | 5.684 | | 1980 | 5.748 | | 1979 | 5.803 | | 1978 | 5.851 | | 1977 | 5.898 | | 1976 | 5.932 | | 1975 | 5.9 | | 1974 | 5.828 | | 1973 | 5.766 | | 1972 | 5.761 | | 1971 | 5.761 | | 1970 | 5.729 | | 1969 | 5.737 | | 1968 | 5.745 | | 1967 | 5.759 | | 1966 | 5.77 | | 1965 | 5.782 | | 1964 | 5.768 | | 1963 | 5.796 | | 1962 | 5.805 | | 1961 | 5.811 | | 1960 | 5.819 |
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