| Year | Value | | 2022 | 50.893451649743 | | 2021 | 50.873350667874 | | 2020 | 50.853140024416 | | 2019 | 50.836536464482 | | 2018 | 50.822608381069 | | 2017 | 50.80835870763 | | 2016 | 50.790584132392 | | 2015 | 50.772662590425 | | 2014 | 50.759187386787 | | 2013 | 50.746322780327 | | 2012 | 50.73106373802 | | 2011 | 50.714802755655 | | 2010 | 50.697680996679 | | 2009 | 50.680096735128 | | 2008 | 50.662478408873 | | 2007 | 50.642997702693 | | 2006 | 50.62121214031 | | 2005 | 50.597956071472 | | 2004 | 50.572449547886 | | 2003 | 50.545384623379 | | 2002 | 50.517940863109 | | 2001 | 50.489710615871 | | 2000 | 50.46199625504 | | 1999 | 50.439066706375 | | 1998 | 50.421032989491 | | 1997 | 50.40349972545 | | 1996 | 50.386058245457 | | 1995 | 50.368455365848 | | 1994 | 50.351310312968 | | 1993 | 50.334802808934 | | 1992 | 50.317800185618 | | 1991 | 50.300620312412 | | 1990 | 50.283180322625 | | 1989 | 50.269361697346 | | 1988 | 50.259821808798 | | 1987 | 50.250361025821 | | 1986 | 50.241480520144 | | 1985 | 50.233638375713 | | 1984 | 50.226609362884 | | 1983 | 50.220176202958 | | 1982 | 50.213690935848 | | 1981 | 50.206630988768 | | 1980 | 50.198931815134 | | 1979 | 50.190256702573 | | 1978 | 50.180463819711 | | 1977 | 50.169751793503 | | 1976 | 50.158507090851 | | 1975 | 50.146479986778 | | 1974 | 50.133093621268 | | 1973 | 50.118117736013 | | 1972 | 50.101947347004 | | 1971 | 50.084852839665 | | 1970 | 50.067004860181 | | 1969 | 50.0485365054 | | 1968 | 50.028803422625 | | 1967 | 50.007980001811 | | 1966 | 49.986607730487 | | 1965 | 49.964633449757 | | 1964 | 49.942154894471 | | 1963 | 49.919191576659 | | 1962 | 49.895303068647 | | 1961 | 49.869660175796 | | 1960 | 49.846994593085 |
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