| Year | Value | | 2021 | 78.445541307963 | | 2020 | 78.843368107184 | | 2019 | 78.823353083564 | | 2018 | 78.653279000008 | | 2017 | 78.340462344407 | | 2016 | 78.123249716315 | | 2015 | 77.881932965178 | | 2014 | 77.648215530005 | | 2013 | 77.397314038299 | | 2012 | 77.127176687895 | | 2011 | 76.840821304786 | | 2010 | 76.557936630599 | | 2009 | 76.353779465499 | | 2008 | 75.708799570658 | | 2007 | 75.833524099786 | | 2006 | 75.561937839548 | | 2005 | 75.21378567189 | | 2004 | 74.636941180899 | | 2003 | 74.620666923185 | | 2002 | 74.110387874982 | | 2001 | 73.788331266925 | | 2000 | 72.940825434404 | | 1999 | 72.507896299289 | | 1998 | 72.44318526379 | | 1997 | 71.92048806617 | | 1996 | 71.533267920929 | | 1995 | 71.318805546857 | | 1994 | 70.959491253091 | | 1993 | 70.795405616502 | | 1992 | 70.204671682553 | | 1991 | 69.625617088013 | | 1990 | 69.584855151202 | | 1989 | 69.411353070457 | | 1988 | 69.087937037575 | | 1987 | 68.781655309327 | | 1986 | 68.426396286387 | | 1985 | 68.032249208314 | | 1984 | 67.645463311329 | | 1983 | 67.263720780825 | | 1982 | 66.807640395372 | | 1981 | 66.312037193811 | | 1980 | 65.814461213474 | | 1979 | 65.249228478132 | | 1978 | 64.623130403 | | 1977 | 63.931460584815 | | 1976 | 63.127873710654 | | 1975 | 62.324803646543 | | 1974 | 61.607772201907 | | 1973 | 60.861625323816 | | 1972 | 59.89258441196 | | 1971 | 59.255597583899 | | 1970 | 58.462812076821 | | 1969 | 57.722922725442 | | 1968 | 57.046906200161 | | 1967 | 56.54575357536 | | 1966 | 55.704547241999 | | 1965 | 54.78350401881 | | 1964 | 54.569125021413 | | 1963 | 53.82919671263 | | 1962 | 53.319960342272 | | 1961 | 45.207180067185 | | 1960 | 39.376250599681 |
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