| Year | Value | | 2021 | 66.989622920209 | | 2020 | 68.255574832298 | | 2019 | 68.771134473647 | | 2018 | 68.496292514519 | | 2017 | 68.377261560554 | | 2016 | 67.905548808368 | | 2015 | 67.288836878099 | | 2014 | 66.709608291593 | | 2013 | 66.212115628942 | | 2012 | 65.632223705378 | | 2011 | 65.075335908798 | | 2010 | 64.552960371014 | | 2009 | 63.814878575395 | | 2008 | 63.191203329688 | | 2007 | 62.497774298752 | | 2006 | 61.797430464785 | | 2005 | 61.201674743498 | | 2004 | 60.849284603807 | | 2003 | 60.570276272349 | | 2002 | 60.428350806414 | | 2001 | 60.39981954896 | | 2000 | 60.432936844397 | | 1999 | 59.935121502901 | | 1998 | 60.304988735473 | | 1997 | 60.710956003312 | | 1996 | 61.107085797806 | | 1995 | 61.264394385872 | | 1994 | 61.432910367279 | | 1993 | 61.774079256584 | | 1992 | 61.840849922131 | | 1991 | 61.989181513151 | | 1990 | 62.046077398241 | | 1989 | 62.029496016317 | | 1988 | 61.432816237153 | | 1987 | 61.261273259228 | | 1986 | 60.870992670747 | | 1985 | 60.525042899093 | | 1984 | 60.168552088921 | | 1983 | 59.689646273822 | | 1982 | 59.368664731843 | | 1981 | 58.931146813458 | | 1980 | 58.579403196464 | | 1979 | 57.887620001606 | | 1978 | 57.470467462236 | | 1977 | 57.314953986572 | | 1976 | 56.742845574565 | | 1975 | 56.471220800578 | | 1974 | 56.091118909278 | | 1973 | 56.580212474431 | | 1972 | 56.17638045911 | | 1971 | 55.571337346002 | | 1970 | 55.008101885559 | | 1969 | 54.574211475804 | | 1968 | 54.72969476189 | | 1967 | 54.43240119702 | | 1966 | 54.148167566986 | | 1965 | 53.844077848702 | | 1964 | 53.253588108944 | | 1963 | 52.726168684135 | | 1962 | 52.70585960245 | | 1961 | 52.331211949067 | | 1960 | 51.931331934281 |
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