| Year | Value | | 2021 | 71.322599648704 | | 2020 | 72.395226763257 | | 2019 | 73.704427947903 | | 2018 | 73.362891403997 | | 2017 | 73.370886267412 | | 2016 | 73.311061735672 | | 2015 | 72.96259175589 | | 2014 | 73.026712893315 | | 2013 | 72.698258817236 | | 2012 | 72.255277650297 | | 2011 | 72.07754922861 | | 2010 | 71.506146642621 | | 2009 | 71.111550156093 | | 2008 | 70.735391766566 | | 2007 | 70.393104524707 | | 2006 | 70.199594563467 | | 2005 | 69.945228896554 | | 2004 | 69.858401449185 | | 2003 | 69.510426421357 | | 2002 | 69.356985697106 | | 2001 | 69.263764353948 | | 2000 | 68.861358203693 | | 1999 | 68.226911621262 | | 1998 | 67.913683884968 | | 1997 | 67.501270926051 | | 1996 | 67.304916737632 | | 1995 | 66.886512252703 | | 1994 | 66.743538103674 | | 1993 | 66.775867694349 | | 1992 | 66.659600797687 | | 1991 | 66.570056238275 | | 1990 | 66.697627241066 | | 1989 | 66.918981123208 | | 1988 | 67.157543935229 | | 1987 | 66.927494340422 | | 1986 | 66.91466849977 | | 1985 | 66.625133861987 | | 1984 | 66.669848922111 | | 1983 | 66.743877406089 | | 1982 | 66.900061999565 | | 1981 | 66.819402863461 | | 1980 | 66.329845998541 | | 1979 | 66.797441250823 | | 1978 | 66.764358082296 | | 1977 | 66.905660956565 | | 1976 | 67.081092941952 | | 1975 | 66.999680774645 | | 1974 | 67.297367437883 | | 1973 | 67.001293917892 | | 1972 | 66.90529711785 | | 1971 | 66.37516619232 | | 1970 | 66.328344148534 | | 1969 | 66.083799172272 | | 1968 | 66.689717643377 | | 1967 | 66.572986158659 | | 1966 | 67.191074257997 | | 1965 | 66.778941568773 | | 1964 | 66.644517904162 | | 1963 | 66.142153782746 | | 1962 | 65.209768946375 | | 1961 | 65.789339592049 | | 1960 | 65.548111181498 |
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