| Year | Value | | 2021 | 2.029 | | 2020 | 2.055 | | 2019 | 2.08 | | 2018 | 2.104 | | 2017 | 2.15 | | 2016 | 2.203 | | 2015 | 2.25 | | 2014 | 2.293 | | 2013 | 2.334 | | 2012 | 2.387 | | 2011 | 2.439 | | 2010 | 2.512 | | 2009 | 2.604 | | 2008 | 2.719 | | 2007 | 2.843 | | 2006 | 2.974 | | 2005 | 3.142 | | 2004 | 3.311 | | 2003 | 3.457 | | 2002 | 3.59 | | 2001 | 3.763 | | 2000 | 3.944 | | 1999 | 4.083 | | 1998 | 4.235 | | 1997 | 4.393 | | 1996 | 4.595 | | 1995 | 4.785 | | 1994 | 4.907 | | 1993 | 5.002 | | 1992 | 5.044 | | 1991 | 5.139 | | 1990 | 5.208 | | 1989 | 5.253 | | 1988 | 5.312 | | 1987 | 5.362 | | 1986 | 5.424 | | 1985 | 5.474 | | 1984 | 5.537 | | 1983 | 5.555 | | 1982 | 5.575 | | 1981 | 5.602 | | 1980 | 5.639 | | 1979 | 5.691 | | 1978 | 5.719 | | 1977 | 5.726 | | 1976 | 5.751 | | 1975 | 5.748 | | 1974 | 5.738 | | 1973 | 5.694 | | 1972 | 5.781 | | 1971 | 5.842 | | 1970 | 5.876 | | 1969 | 5.912 | | 1968 | 5.969 | | 1967 | 5.98 | | 1966 | 6.001 | | 1965 | 6.029 | | 1964 | 6.065 | | 1963 | 6.065 | | 1962 | 6.075 | | 1961 | 6.063 | | 1960 | 6.03 |
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