| Year | Value | | 2021 | 3.491 | | 2020 | 3.548 | | 2019 | 3.615 | | 2018 | 3.679 | | 2017 | 3.752 | | 2016 | 3.817 | | 2015 | 3.889 | | 2014 | 3.953 | | 2013 | 4.019 | | 2012 | 4.086 | | 2011 | 4.151 | | 2010 | 4.153 | | 2009 | 4.138 | | 2008 | 4.118 | | 2007 | 4.142 | | 2006 | 4.17 | | 2005 | 4.21 | | 2004 | 4.252 | | 2003 | 4.299 | | 2002 | 4.36 | | 2001 | 4.417 | | 2000 | 4.469 | | 1999 | 4.502 | | 1998 | 4.576 | | 1997 | 4.657 | | 1996 | 4.742 | | 1995 | 4.884 | | 1994 | 5.044 | | 1993 | 5.186 | | 1992 | 5.289 | | 1991 | 5.373 | | 1990 | 5.459 | | 1989 | 5.55 | | 1988 | 5.623 | | 1987 | 5.667 | | 1986 | 5.688 | | 1985 | 5.713 | | 1984 | 5.733 | | 1983 | 5.759 | | 1982 | 5.74 | | 1981 | 5.726 | | 1980 | 5.664 | | 1979 | 5.608 | | 1978 | 5.568 | | 1977 | 5.516 | | 1976 | 5.457 | | 1975 | 5.391 | | 1974 | 5.327 | | 1973 | 5.287 | | 1972 | 5.237 | | 1971 | 5.163 | | 1970 | 5.097 | | 1969 | 5.049 | | 1968 | 4.984 | | 1967 | 4.919 | | 1966 | 4.861 | | 1965 | 4.785 | | 1964 | 4.713 | | 1963 | 4.649 | | 1962 | 4.587 | | 1961 | 4.504 | | 1960 | 4.422 |
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