| Year | Value | | 2021 | 65.036436414065 | | 2020 | 66.663507229195 | | 2019 | 67.329452064355 | | 2018 | 67.169195846011 | | 2017 | 66.926988498389 | | 2016 | 66.626192243892 | | 2015 | 66.214316485961 | | 2014 | 65.781186638637 | | 2013 | 65.299582286723 | | 2012 | 64.905493073654 | | 2011 | 64.517906159275 | | 2010 | 64.10104727367 | | 2009 | 63.744278151167 | | 2008 | 63.348238980667 | | 2007 | 63.188494255641 | | 2006 | 62.958280498811 | | 2005 | 62.625942091759 | | 2004 | 62.316599479328 | | 2003 | 62.013780962629 | | 2002 | 61.71428785111 | | 2001 | 61.33984726574 | | 2000 | 61.038944809147 | | 1999 | 60.777951851612 | | 1998 | 60.318400661989 | | 1997 | 59.891410206893 | | 1996 | 59.543294966176 | | 1995 | 59.234748947849 | | 1994 | 58.957102359297 | | 1993 | 58.703083743719 | | 1992 | 58.455177777957 | | 1991 | 58.082763139613 | | 1990 | 57.88542326662 | | 1989 | 57.617226449862 | | 1988 | 57.201172878445 | | 1987 | 56.883739467511 | | 1986 | 56.53376909443 | | 1985 | 56.099453331917 | | 1984 | 55.6959222494 | | 1983 | 55.220196136184 | | 1982 | 54.780773793148 | | 1981 | 54.407282344301 | | 1980 | 54.084850692628 | | 1979 | 53.65850498385 | | 1978 | 53.217675251872 | | 1977 | 52.86191786819 | | 1976 | 52.364546824966 | | 1975 | 51.885924225162 | | 1974 | 51.255329260771 | | 1973 | 50.85077625583 | | 1972 | 50.289931020987 | | 1971 | 48.091156514811 | | 1970 | 49.317771748912 | | 1969 | 49.316092305802 | | 1968 | 48.9147620602 | | 1967 | 47.980695614819 | | 1966 | 47.779510320179 | | 1965 | 47.348714548879 | | 1964 | 47.892229223727 | | 1963 | 47.49805586771 | | 1962 | 47.147028451984 | | 1961 | 46.77685548187 | | 1960 | 46.438461658239 |
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