| Year | Value | | 2021 | 3.215 | | 2020 | 3.274 | | 2019 | 3.322 | | 2018 | 3.382 | | 2017 | 3.432 | | 2016 | 3.495 | | 2015 | 3.558 | | 2014 | 3.625 | | 2013 | 3.684 | | 2012 | 3.746 | | 2011 | 3.816 | | 2010 | 3.883 | | 2009 | 3.941 | | 2008 | 4.015 | | 2007 | 4.076 | | 2006 | 4.148 | | 2005 | 4.22 | | 2004 | 4.283 | | 2003 | 4.362 | | 2002 | 4.419 | | 2001 | 4.469 | | 2000 | 4.525 | | 1999 | 4.587 | | 1998 | 4.632 | | 1997 | 4.679 | | 1996 | 4.728 | | 1995 | 4.78 | | 1994 | 4.87 | | 1993 | 4.962 | | 1992 | 5.033 | | 1991 | 5.109 | | 1990 | 5.18 | | 1989 | 5.243 | | 1988 | 5.302 | | 1987 | 5.359 | | 1986 | 5.415 | | 1985 | 5.47 | | 1984 | 5.514 | | 1983 | 5.563 | | 1982 | 5.587 | | 1981 | 5.645 | | 1980 | 5.705 | | 1979 | 5.785 | | 1978 | 5.879 | | 1977 | 5.957 | | 1976 | 6.018 | | 1975 | 6.065 | | 1974 | 6.114 | | 1973 | 6.16 | | 1972 | 6.197 | | 1971 | 6.229 | | 1970 | 6.25 | | 1969 | 6.258 | | 1968 | 6.252 | | 1967 | 6.242 | | 1966 | 6.232 | | 1965 | 6.203 | | 1964 | 6.191 | | 1963 | 6.153 | | 1962 | 6.135 | | 1961 | 6.074 | | 1960 | 6.018 |
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