| Year | Value | | 2021 | 68.466040591999 | | 2020 | 70.028693413879 | | 2019 | 71.014738884004 | | 2018 | 70.794825026464 | | 2017 | 70.538449031191 | | 2016 | 70.216387809045 | | 2015 | 69.871207915862 | | 2014 | 69.484991507761 | | 2013 | 69.065320395544 | | 2012 | 68.672553271452 | | 2011 | 68.291769774435 | | 2010 | 67.86597309302 | | 2009 | 67.527998477828 | | 2008 | 67.079690048916 | | 2007 | 66.884711731743 | | 2006 | 66.592029582935 | | 2005 | 66.191503483995 | | 2004 | 65.742901991285 | | 2003 | 65.519687292374 | | 2002 | 65.222654908252 | | 2001 | 64.816354985673 | | 2000 | 64.499257082645 | | 1999 | 64.143612998811 | | 1998 | 63.710093816219 | | 1997 | 63.284362591726 | | 1996 | 62.876756098541 | | 1995 | 62.56732057838 | | 1994 | 62.157122558847 | | 1993 | 61.901353791222 | | 1992 | 61.620556411048 | | 1991 | 61.135431520971 | | 1990 | 60.827546768003 | | 1989 | 60.466286593872 | | 1988 | 60.027341549162 | | 1987 | 59.622416457942 | | 1986 | 59.032760171447 | | 1985 | 58.566583627407 | | 1984 | 58.051581934102 | | 1983 | 57.479656691082 | | 1982 | 57.04267189772 | | 1981 | 56.552845776687 | | 1980 | 56.117215264625 | | 1979 | 55.566752730975 | | 1978 | 54.979059155929 | | 1977 | 54.48752497735 | | 1976 | 53.884096032353 | | 1975 | 53.347441472684 | | 1974 | 52.923451776978 | | 1973 | 52.463611250107 | | 1972 | 52.002368013282 | | 1971 | 50.173850233769 | | 1970 | 50.769121366703 | | 1969 | 50.822116537861 | | 1968 | 50.399518961139 | | 1967 | 49.351341735588 | | 1966 | 48.669992992792 | | 1965 | 47.679669659579 | | 1964 | 48.670698597538 | | 1963 | 48.187870192688 | | 1962 | 47.789551935947 | | 1961 | 47.365520100693 | | 1960 | 46.879243730023 |
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