| Year | Value | | 2022 | 49.764781018993 | | 2021 | 49.749016124686 | | 2020 | 49.734540420118 | | 2019 | 49.723857027944 | | 2018 | 49.71361593676 | | 2017 | 49.704362236068 | | 2016 | 49.694259539654 | | 2015 | 49.683314629831 | | 2014 | 49.676209051229 | | 2013 | 49.670551487147 | | 2012 | 49.66665883194 | | 2011 | 49.666039625006 | | 2010 | 49.66651292388 | | 2009 | 49.666307938561 | | 2008 | 49.668505101023 | | 2007 | 49.675790404151 | | 2006 | 49.689301370731 | | 2005 | 49.708230056716 | | 2004 | 49.731630482697 | | 2003 | 49.759094165196 | | 2002 | 49.789330621951 | | 2001 | 49.825279823223 | | 2000 | 49.866589572986 | | 1999 | 49.897490808624 | | 1998 | 49.922823556259 | | 1997 | 49.957031676135 | | 1996 | 49.991137812384 | | 1995 | 50.017735933147 | | 1994 | 50.044279767295 | | 1993 | 50.076920828934 | | 1992 | 50.109837133495 | | 1991 | 50.162565434385 | | 1990 | 50.211830789431 | | 1989 | 50.237516471681 | | 1988 | 50.273806541437 | | 1987 | 50.318992432481 | | 1986 | 50.357468086898 | | 1985 | 50.386813372846 | | 1984 | 50.403625855135 | | 1983 | 50.408203835906 | | 1982 | 50.413653492978 | | 1981 | 50.422068339224 | | 1980 | 50.430286112343 | | 1979 | 50.435631839433 | | 1978 | 50.433151050678 | | 1977 | 50.425445684582 | | 1976 | 50.417570316521 | | 1975 | 50.410697892334 | | 1974 | 50.408873201243 | | 1973 | 50.411040272082 | | 1972 | 50.415009998887 | | 1971 | 50.420249849534 | | 1970 | 50.427221806678 | | 1969 | 50.433931406996 | | 1968 | 50.438694582584 | | 1967 | 50.443600461177 | | 1966 | 50.447691265285 | | 1965 | 50.45128287503 | | 1964 | 50.453428505536 | | 1963 | 50.454392918344 | | 1962 | 50.455563102618 | | 1961 | 50.455223855478 | | 1960 | 50.453607706819 |
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