| Year | Value | | 2021 | 59.571870421618 | | 2020 | 59.559661403223 | | 2019 | 59.539313039232 | | 2018 | 59.506755656845 | | 2017 | 59.396874491291 | | 2016 | 59.274784307342 | | 2015 | 59.193390851375 | | 2014 | 59.144554777796 | | 2013 | 59.010255575452 | | 2012 | 58.603288295621 | | 2011 | 58.19632101579 | | 2010 | 58.19632101579 | | 2009 | 57.992837375875 | | 2008 | 57.952140647892 | | 2007 | 57.707960279994 | | 2006 | 57.504476640078 | | 2005 | 57.467849584893 | | 2004 | 57.47598893049 | | 2003 | 57.431222529709 | | 2002 | 57.345759400944 | | 2001 | 57.300993000163 | | 2000 | 57.296923327365 | | 1999 | 57.292853654566 | | 1998 | 57.248087253785 | | 1997 | 57.121927397037 | | 1996 | 57.117857724239 | | 1995 | 57.073091323458 | | 1994 | 57.170763470617 | | 1993 | 57.18704216181 | | 1992 | 57.199251180205 | | 1991 | 57.174833143415 | | 1990 | 57.54924304086 | | 1989 | 57.207390525802 | | 1988 | 57.305062672961 | | 1987 | 57.276574963373 | | 1986 | 57.374247110532 | | 1985 | 57.471919257692 | | 1984 | 57.528894676868 | | 1983 | 57.622497151229 | | 1982 | 57.679472570405 | | 1981 | 57.777144717565 | | 1980 | 57.874816864724 | | 1979 | 57.972489011883 | | 1978 | 57.984698030278 | | 1977 | 58.082370177438 | | 1976 | 58.180042324597 | | 1975 | 58.277714471756 | | 1974 | 58.334689890933 | | 1973 | 58.428292365294 | | 1972 | 58.525964512453 | | 1971 | 58.623636659613 | | 1970 | 58.721308806772 | | 1969 | 58.814911281133 | | 1968 | 58.912583428292 | | 1967 | 59.010255575452 | | 1966 | 59.107927722611 | | 1965 | 59.205599869771 | | 1964 | 59.299202344132 | | 1963 | 59.396874491291 | | 1962 | 59.49454663845 | | 1961 | 59.498616311249 |
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