| Year | Value | | 2022 | 50.502642463235 | | 2021 | 50.520025016794 | | 2020 | 50.566295759503 | | 2019 | 50.650201583151 | | 2018 | 50.762893254732 | | 2017 | 50.857675499655 | | 2016 | 50.896952742776 | | 2015 | 50.922991553117 | | 2014 | 50.95734962371 | | 2013 | 50.990957163866 | | 2012 | 51.025721850965 | | 2011 | 51.049309964643 | | 2010 | 51.071476362524 | | 2009 | 51.096198304649 | | 2008 | 51.129625313965 | | 2007 | 51.167571659792 | | 2006 | 51.204732077061 | | 2005 | 51.253614921334 | | 2004 | 51.310703633859 | | 2003 | 51.363740545496 | | 2002 | 51.423213084455 | | 2001 | 51.488592478979 | | 2000 | 51.536756912997 | | 1999 | 51.579645192699 | | 1998 | 51.629903405427 | | 1997 | 51.682004054365 | | 1996 | 51.73584139847 | | 1995 | 51.760299100034 | | 1994 | 51.755167935984 | | 1993 | 51.742216599902 | | 1992 | 51.73261226243 | | 1991 | 51.730739343591 | | 1990 | 51.735051671041 | | 1989 | 51.74605682765 | | 1988 | 51.744262009494 | | 1987 | 51.728996653555 | | 1986 | 51.720224319032 | | 1985 | 51.74785873255 | | 1984 | 51.789551741881 | | 1983 | 51.827600433979 | | 1982 | 51.875568997176 | | 1981 | 51.904506229039 | | 1980 | 51.876797099637 | | 1979 | 51.811874760463 | | 1978 | 51.751039814517 | | 1977 | 51.702975891512 | | 1976 | 51.664672732424 | | 1975 | 51.637353334441 | | 1974 | 51.608944424079 | | 1973 | 51.567910657615 | | 1972 | 51.531439504491 | | 1971 | 51.509049384838 | | 1970 | 51.506987430064 | | 1969 | 51.519372732202 | | 1968 | 51.533199669772 | | 1967 | 51.54304692157 | | 1966 | 51.546311846015 | | 1965 | 51.553124972787 | | 1964 | 51.572266140817 | | 1963 | 51.591495418557 | | 1962 | 51.607192602511 | | 1961 | 51.666137446133 | | 1960 | 51.869728081182 |
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