| Year | Value | | 2021 | 71.899875725744 | | 2020 | 72.172696996573 | | 2019 | 73.143918592596 | | 2018 | 72.984373417475 | | 2017 | 72.767001139756 | | 2016 | 72.256488376844 | | 2015 | 71.986189124277 | | 2014 | 71.702779027554 | | 2013 | 71.405746812826 | | 2012 | 71.377647146233 | | 2011 | 71.522858458161 | | 2010 | 71.276841858768 | | 2009 | 71.022219046739 | | 2008 | 70.683539861407 | | 2007 | 70.425840479211 | | 2006 | 70.091654959821 | | 2005 | 69.907371819194 | | 2004 | 69.624766265689 | | 2003 | 69.143346882808 | | 2002 | 69.326067519651 | | 2001 | 68.973295217576 | | 2000 | 68.64149747381 | | 1999 | 68.283481473543 | | 1998 | 67.852799095159 | | 1997 | 67.633855993929 | | 1996 | 67.357344554015 | | 1995 | 66.96619722403 | | 1994 | 66.648140853537 | | 1993 | 66.46992883964 | | 1992 | 66.157199489111 | | 1991 | 65.582706462272 | | 1990 | 64.351246681832 | | 1989 | 64.334166634891 | | 1988 | 63.39417594761 | | 1987 | 63.022849021656 | | 1986 | 62.30619830134 | | 1985 | 61.734356522955 | | 1984 | 60.938541998694 | | 1983 | 59.627497286313 | | 1982 | 58.049706816106 | | 1981 | 57.574552521244 | | 1980 | 57.717093644241 | | 1979 | 57.364740197397 | | 1978 | 56.136016042455 | | 1977 | 55.599572709853 | | 1976 | 54.281658444633 | | 1975 | 53.846006349485 | | 1974 | 53.243756535535 | | 1973 | 52.434055017107 | | 1972 | 51.863309479731 | | 1971 | 51.297512076688 | | 1970 | 50.629303447558 | | 1969 | 50.057712209392 | | 1968 | 49.453752599998 | | 1967 | 49.028916251094 | | 1966 | 48.557819657797 | | 1965 | 48.04629863289 | | 1964 | 47.443875806025 | | 1963 | 46.771594953839 | | 1962 | 45.610731155372 | | 1961 | 45.336940234722 | | 1960 | 44.621149338016 |
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