| Year | Value | | 2022 | 52.058191177163 | | 2021 | 52.084712458889 | | 2020 | 52.129030894721 | | 2019 | 51.712263149446 | | 2018 | 52.428514199716 | | 2017 | 53.75924068935 | | 2016 | 53.790288100551 | | 2015 | 53.844384686151 | | 2014 | 53.930665079601 | | 2013 | 54.051499975923 | | 2012 | 54.209871422646 | | 2011 | 54.255707367158 | | 2010 | 54.17681013929 | | 2009 | 54.105470989109 | | 2008 | 54.038179148311 | | 2007 | 53.970904357772 | | 2006 | 53.900737652341 | | 2005 | 53.834296462791 | | 2004 | 53.781628447165 | | 2003 | 53.739832853509 | | 2002 | 53.718295115361 | | 2001 | 53.698686633815 | | 2000 | 53.607591356488 | | 1999 | 53.450935770082 | | 1998 | 53.285370051635 | | 1997 | 53.12446906113 | | 1996 | 52.96969208664 | | 1995 | 52.826843391415 | | 1994 | 52.692173661474 | | 1993 | 52.566384374165 | | 1992 | 52.455044825621 | | 1991 | 52.356132394966 | | 1990 | 52.266381894677 | | 1989 | 52.182984214209 | | 1988 | 52.098460039861 | | 1987 | 52.013285379683 | | 1986 | 51.931508775518 | | 1985 | 51.856178857117 | | 1984 | 51.779268650434 | | 1983 | 51.701707441386 | | 1982 | 51.628164637563 | | 1981 | 51.548807825555 | | 1980 | 51.465403472085 | | 1979 | 51.388498582122 | | 1978 | 51.312917986624 | | 1977 | 51.240098771767 | | 1976 | 51.171327547412 | | 1975 | 51.100540763514 | | 1974 | 51.030777883366 | | 1973 | 50.967578652269 | | 1972 | 50.893725323849 | | 1971 | 50.821894371109 | | 1970 | 50.767696246301 | | 1969 | 50.71737507315 | | 1968 | 50.671769344438 | | 1967 | 50.626737584249 | | 1966 | 50.579663529445 | | 1965 | 50.534211515147 | | 1964 | 50.486777204159 | | 1963 | 50.436584067052 | | 1962 | 50.385284429476 | | 1961 | 50.33054871086 | | 1960 | 50.259000259 |
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