| Year | Value | | 2022 | 50.681430448766 | | 2021 | 50.658238418314 | | 2020 | 50.652011959316 | | 2019 | 50.53162758108 | | 2018 | 50.588120360814 | | 2017 | 50.7614937573 | | 2016 | 50.744488984775 | | 2015 | 50.71830332898 | | 2014 | 50.69606200208 | | 2013 | 50.681842317327 | | 2012 | 50.67097695223 | | 2011 | 50.660413233616 | | 2010 | 50.644687356413 | | 2009 | 50.623862128718 | | 2008 | 50.603854242129 | | 2007 | 50.59005921894 | | 2006 | 50.580898368023 | | 2005 | 50.565893029966 | | 2004 | 50.544971539232 | | 2003 | 50.52705925464 | | 2002 | 50.508706027799 | | 2001 | 50.492429590749 | | 2000 | 50.483372278849 | | 1999 | 50.481702827974 | | 1998 | 50.479671428096 | | 1997 | 50.479490142022 | | 1996 | 50.477526849465 | | 1995 | 50.472159055284 | | 1994 | 50.468152203062 | | 1993 | 50.464460646041 | | 1992 | 50.465499081293 | | 1991 | 50.465905671732 | | 1990 | 50.470739460474 | | 1989 | 50.474840989962 | | 1988 | 50.478655153768 | | 1987 | 50.481711684351 | | 1986 | 50.48398102551 | | 1985 | 50.490962964198 | | 1984 | 50.497110353519 | | 1983 | 50.507610096024 | | 1982 | 50.516964239418 | | 1981 | 50.529493871943 | | 1980 | 50.548742210857 | | 1979 | 50.564051388552 | | 1978 | 50.583501813383 | | 1977 | 50.604006867013 | | 1976 | 50.613564160585 | | 1975 | 50.623282167176 | | 1974 | 50.645059891896 | | 1973 | 50.668979887255 | | 1972 | 50.69232827031 | | 1971 | 50.716306880106 | | 1970 | 50.737291306414 | | 1969 | 50.697292779178 | | 1968 | 50.593314656727 | | 1967 | 50.479814917321 | | 1966 | 50.356620365606 | | 1965 | 50.239428215694 | | 1964 | 50.139314801089 | | 1963 | 50.047679628545 | | 1962 | 49.953319213766 | | 1961 | 49.855264800677 | | 1960 | 49.801962781989 |
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