| Year | Value | | 2021 | 68.885707677759 | | 2020 | 69.799410362522 | | 2019 | 70.623134051809 | | 2018 | 70.431682418566 | | 2017 | 70.169810281576 | | 2016 | 69.995379313613 | | 2015 | 69.759333733021 | | 2014 | 69.522937583331 | | 2013 | 69.192405516337 | | 2012 | 68.904583958972 | | 2011 | 68.638752759029 | | 2010 | 68.309859318853 | | 2009 | 68.034991150786 | | 2008 | 67.659238373728 | | 2007 | 67.470991610694 | | 2006 | 67.224198285254 | | 2005 | 66.871871554345 | | 2004 | 66.560119664601 | | 2003 | 66.306274902141 | | 2002 | 66.050964552659 | | 2001 | 65.764017209596 | | 2000 | 65.473064205771 | | 1999 | 65.167135043628 | | 1998 | 64.830932865102 | | 1997 | 64.578293863343 | | 1996 | 64.22964630184 | | 1995 | 63.915495736985 | | 1994 | 63.716888290195 | | 1993 | 63.445523325027 | | 1992 | 63.290150502459 | | 1991 | 63.0372741714 | | 1990 | 62.828551695204 | | 1989 | 62.681064445511 | | 1988 | 62.331109928862 | | 1987 | 62.180012708583 | | 1986 | 61.887108615651 | | 1985 | 61.484353403647 | | 1984 | 61.170500102691 | | 1983 | 60.866916317485 | | 1982 | 60.628910317951 | | 1981 | 60.288286647386 | | 1980 | 59.9497259839 | | 1979 | 59.645247356122 | | 1978 | 59.259845077597 | | 1977 | 58.945077173331 | | 1976 | 58.515473308118 | | 1975 | 58.064195561034 | | 1974 | 57.625184867122 | | 1973 | 57.232639775309 | | 1972 | 56.733923506488 | | 1971 | 55.775310634416 | | 1970 | 55.782687379687 | | 1969 | 55.459519177225 | | 1968 | 55.139863300914 | | 1967 | 54.72541792431 | | 1966 | 54.338477957406 | | 1965 | 53.765644378162 | | 1964 | 54.03135461715 | | 1963 | 53.558891349043 | | 1962 | 53.240644469015 | | 1961 | 50.93548621388 | | 1960 | 49.02661854285 |
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