| Year | Value | | 2022 | 50.437174692208 | | 2021 | 50.421883614064 | | 2020 | 50.408173158121 | | 2019 | 50.399462625696 | | 2018 | 50.384098717474 | | 2017 | 50.363518431764 | | 2016 | 50.349272685249 | | 2015 | 50.335536835031 | | 2014 | 50.318325484609 | | 2013 | 50.305683771843 | | 2012 | 50.295765845917 | | 2011 | 50.285252935935 | | 2010 | 50.279524046197 | | 2009 | 50.282114625436 | | 2008 | 50.290368757208 | | 2007 | 50.302277061055 | | 2006 | 50.315750036973 | | 2005 | 50.331328200394 | | 2004 | 50.349872309124 | | 2003 | 50.369528087114 | | 2002 | 50.389780933228 | | 2001 | 50.410409095273 | | 2000 | 50.429935478886 | | 1999 | 50.445629651719 | | 1998 | 50.456775907698 | | 1997 | 50.464066333609 | | 1996 | 50.468529971463 | | 1995 | 50.472155151505 | | 1994 | 50.475239980923 | | 1993 | 50.477015638495 | | 1992 | 50.477274586513 | | 1991 | 50.478126835028 | | 1990 | 50.481513706624 | | 1989 | 50.48719608619 | | 1988 | 50.494018298796 | | 1987 | 50.501669037598 | | 1986 | 50.510277850485 | | 1985 | 50.51759544865 | | 1984 | 50.524204540074 | | 1983 | 50.531363387098 | | 1982 | 50.536522116343 | | 1981 | 50.537985252201 | | 1980 | 50.541813357333 | | 1979 | 50.548342757099 | | 1978 | 50.551078206 | | 1977 | 50.552528560412 | | 1976 | 50.556024038119 | | 1975 | 50.56271987769 | | 1974 | 50.567924792803 | | 1973 | 50.568018805046 | | 1972 | 50.564448977648 | | 1971 | 50.558933818057 | | 1970 | 50.555704842123 | | 1969 | 50.554447368376 | | 1968 | 50.551820037108 | | 1967 | 50.54799164166 | | 1966 | 50.543054626806 | | 1965 | 50.535493166923 | | 1964 | 50.525217944142 | | 1963 | 50.511785402198 | | 1962 | 50.494931714632 | | 1961 | 50.474372691045 | | 1960 | 50.449174894713 |
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