| Year | Value | | 2021 | 68.876451714771 | | 2020 | 70.231404260362 | | 2019 | 70.510582115788 | | 2018 | 70.161372751708 | | 2017 | 70.139207158686 | | 2016 | 69.610728876441 | | 2015 | 68.967416602397 | | 2014 | 68.462272002661 | | 2013 | 67.921127371321 | | 2012 | 67.298963228126 | | 2011 | 66.734670042333 | | 2010 | 66.132601372642 | | 2009 | 65.362014047171 | | 2008 | 64.771741645768 | | 2007 | 64.161896285787 | | 2006 | 63.527421095908 | | 2005 | 63.005404083224 | | 2004 | 62.699059901452 | | 2003 | 62.392136654653 | | 2002 | 62.376433139264 | | 2001 | 62.371866141221 | | 2000 | 62.458465949595 | | 1999 | 62.22698617964 | | 1998 | 62.705065497419 | | 1997 | 63.137682318088 | | 1996 | 63.570786540391 | | 1995 | 63.895529337498 | | 1994 | 64.007085673631 | | 1993 | 64.39956600431 | | 1992 | 64.562996708806 | | 1991 | 64.703190067457 | | 1990 | 64.753589510431 | | 1989 | 64.648043078996 | | 1988 | 64.46485171488 | | 1987 | 64.289149731293 | | 1986 | 63.933993485854 | | 1985 | 63.647276241994 | | 1984 | 63.307429253425 | | 1983 | 62.829709731477 | | 1982 | 62.523223774103 | | 1981 | 62.1693891305 | | 1980 | 61.832406438493 | | 1979 | 60.912566743901 | | 1978 | 60.467447150578 | | 1977 | 60.305198311047 | | 1976 | 59.780582086656 | | 1975 | 59.435894478095 | | 1974 | 59.515579445451 | | 1973 | 59.327575488966 | | 1972 | 58.957625111717 | | 1971 | 58.372440588823 | | 1970 | 57.792833184703 | | 1969 | 57.340886457093 | | 1968 | 57.440195826462 | | 1967 | 57.121852025308 | | 1966 | 56.824369168102 | | 1965 | 56.535400659666 | | 1964 | 56.016632454141 | | 1963 | 55.536349104333 | | 1962 | 55.303651071675 | | 1961 | 54.950432699802 | | 1960 | 54.605134440172 |
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