| Year | Value | | 2021 | 69.779528132526 | | 2020 | 70.82146154497 | | 2019 | 71.525095569987 | | 2018 | 71.321107049324 | | 2017 | 71.042290589097 | | 2016 | 70.80497556982 | | 2015 | 70.5234705053 | | 2014 | 70.2364937647 | | 2013 | 69.911003281191 | | 2012 | 69.585815398951 | | 2011 | 69.269631772652 | | 2010 | 68.900448124289 | | 2009 | 68.603280453153 | | 2008 | 68.179423160393 | | 2007 | 67.995781745325 | | 2006 | 67.716993634646 | | 2005 | 67.321737311434 | | 2004 | 66.925120584484 | | 2003 | 66.688696499841 | | 2002 | 66.407507010969 | | 2001 | 66.084890092411 | | 2000 | 65.704576839026 | | 1999 | 65.365805358266 | | 1998 | 65.023335987189 | | 1997 | 64.707878653268 | | 1996 | 64.341914111612 | | 1995 | 64.08025214999 | | 1994 | 63.792902693677 | | 1993 | 63.529832927419 | | 1992 | 63.301784062027 | | 1991 | 63.020161794493 | | 1990 | 62.86084197339 | | 1989 | 62.665356358886 | | 1988 | 62.279182773778 | | 1987 | 62.059945655269 | | 1986 | 61.719146304741 | | 1985 | 61.254700895642 | | 1984 | 60.886808826819 | | 1983 | 60.549689354525 | | 1982 | 60.238958962066 | | 1981 | 59.836900368033 | | 1980 | 59.417500945422 | | 1979 | 58.985066667543 | | 1978 | 58.514109346786 | | 1977 | 58.068940989328 | | 1976 | 57.518621996316 | | 1975 | 56.976814144025 | | 1974 | 56.45773027069 | | 1973 | 55.987905487165 | | 1972 | 55.353076659926 | | 1971 | 54.315723868829 | | 1970 | 54.206288730782 | | 1969 | 53.849032758969 | | 1968 | 53.454683326336 | | 1967 | 52.793605220736 | | 1966 | 52.319530350249 | | 1965 | 51.668051117857 | | 1964 | 51.880499423863 | | 1963 | 51.337600472818 | | 1962 | 50.893897800703 | | 1961 | 47.749930479054 | | 1960 | 45.320120168776 |
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