| Year | Value | | 2021 | 67.822438943878 | | 2020 | 69.082572530333 | | 2019 | 69.467199622489 | | 2018 | 69.26893495592 | | 2017 | 69.180603205957 | | 2016 | 68.807698330213 | | 2015 | 68.347291796031 | | 2014 | 67.94508486662 | | 2013 | 67.595659151213 | | 2012 | 67.161784872776 | | 2011 | 66.704323995768 | | 2010 | 66.257671213147 | | 2009 | 65.670706845111 | | 2008 | 65.113122137924 | | 2007 | 64.594800831359 | | 2006 | 64.050738279096 | | 2005 | 63.59498856728 | | 2004 | 63.296411416214 | | 2003 | 63.010062491993 | | 2002 | 62.941058052719 | | 2001 | 62.893443819464 | | 2000 | 62.910126900661 | | 1999 | 62.523693163878 | | 1998 | 62.82291579858 | | 1997 | 63.09708622714 | | 1996 | 63.416665175337 | | 1995 | 63.538921116187 | | 1994 | 63.640828936287 | | 1993 | 63.89562444158 | | 1992 | 63.920590874369 | | 1991 | 64.02202032707 | | 1990 | 64.046076620373 | | 1989 | 64.016935717671 | | 1988 | 63.543120980976 | | 1987 | 63.371678463869 | | 1986 | 63.044596273478 | | 1985 | 62.754541290085 | | 1984 | 62.4708807911 | | 1983 | 62.103955348829 | | 1982 | 61.862274686713 | | 1981 | 61.512211202617 | | 1980 | 61.206888866719 | | 1979 | 60.71464410985 | | 1978 | 60.369928695236 | | 1977 | 60.174288273622 | | 1976 | 59.761383378525 | | 1975 | 59.533631814316 | | 1974 | 59.259094987632 | | 1973 | 59.415301802355 | | 1972 | 59.070913974712 | | 1971 | 58.63778724138 | | 1970 | 58.22587883803 | | 1969 | 57.844505773394 | | 1968 | 57.895045716226 | | 1967 | 57.675848057935 | | 1966 | 57.388346340293 | | 1965 | 57.073984417494 | | 1964 | 56.536012652835 | | 1963 | 56.064062851744 | | 1962 | 55.84878420362 | | 1961 | 55.412229994705 | | 1960 | 55.045272154472 |
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