| Year | Value | | 2021 | 69.933572695128 | | 2020 | 71.270209658925 | | 2019 | 71.461888709079 | | 2018 | 71.22797725104 | | 2017 | 71.201235930266 | | 2016 | 70.779917699606 | | 2015 | 70.286130182836 | | 2014 | 69.904577670006 | | 2013 | 69.514920701046 | | 2012 | 69.066647983223 | | 2011 | 68.659953901035 | | 2010 | 68.182892215959 | | 2009 | 67.581674265347 | | 2008 | 67.030106657631 | | 2007 | 66.576272701381 | | 2006 | 66.098959615805 | | 2005 | 65.722163978783 | | 2004 | 65.451423194632 | | 2003 | 65.110012784885 | | 2002 | 65.131784923157 | | 2001 | 65.056843579409 | | 2000 | 65.088916231964 | | 1999 | 64.869488363074 | | 1998 | 65.259144086451 | | 1997 | 65.509590966439 | | 1996 | 65.895459127509 | | 1995 | 66.089572475695 | | 1994 | 66.159911410594 | | 1993 | 66.421258085047 | | 1992 | 66.516314008263 | | 1991 | 66.627229756119 | | 1990 | 66.611709456848 | | 1989 | 66.549934022623 | | 1988 | 66.332050224983 | | 1987 | 66.183394064737 | | 1986 | 65.872220508903 | | 1985 | 65.607387546392 | | 1984 | 65.336442392137 | | 1983 | 64.955501146729 | | 1982 | 64.73350762475 | | 1981 | 64.409300007575 | | 1980 | 64.128868745997 | | 1979 | 63.491778614814 | | 1978 | 63.106808906314 | | 1977 | 62.928917059816 | | 1976 | 62.582430990022 | | 1975 | 62.285908505905 | | 1974 | 62.274504870343 | | 1973 | 62.020803290994 | | 1972 | 61.665642532361 | | 1971 | 61.243726361069 | | 1970 | 60.812316114986 | | 1969 | 60.38975737078 | | 1968 | 60.381446309584 | | 1967 | 60.151760623096 | | 1966 | 59.8290960491 | | 1965 | 59.497260245589 | | 1964 | 58.979639645486 | | 1963 | 58.556171295298 | | 1962 | 58.177784042539 | | 1961 | 57.741297174491 | | 1960 | 57.42227889929 |
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