| Year | Value | | 2022 | 50.567204176754 | | 2021 | 50.575860752108 | | 2020 | 50.581429508104 | | 2019 | 50.587082278284 | | 2018 | 50.598006482794 | | 2017 | 50.609914279275 | | 2016 | 50.619051966532 | | 2015 | 50.624917887198 | | 2014 | 50.630564228149 | | 2013 | 50.638664034923 | | 2012 | 50.645884010824 | | 2011 | 50.637990645163 | | 2010 | 50.629824988336 | | 2009 | 50.637878611663 | | 2008 | 50.648466703051 | | 2007 | 50.658302962627 | | 2006 | 50.667297782566 | | 2005 | 50.675549675366 | | 2004 | 50.677435576159 | | 2003 | 50.671946653412 | | 2002 | 50.658619091959 | | 2001 | 50.643772229053 | | 2000 | 50.632761419141 | | 1999 | 50.617534756844 | | 1998 | 50.597347448049 | | 1997 | 50.576312158655 | | 1996 | 50.555614148635 | | 1995 | 50.537117979878 | | 1994 | 50.517269802827 | | 1993 | 50.492866010016 | | 1992 | 50.468751495062 | | 1991 | 50.448850653235 | | 1990 | 50.425144757556 | | 1989 | 50.392301968788 | | 1988 | 50.360229462184 | | 1987 | 50.331894629655 | | 1986 | 50.307674504081 | | 1985 | 50.283022112768 | | 1984 | 50.253544615 | | 1983 | 50.222638522277 | | 1982 | 50.196578780019 | | 1981 | 50.177363602099 | | 1980 | 50.162222497126 | | 1979 | 50.155857773906 | | 1978 | 50.159923953444 | | 1977 | 50.168882368777 | | 1976 | 50.191833095623 | | 1975 | 50.225229360827 | | 1974 | 50.257002475114 | | 1973 | 50.293210465212 | | 1972 | 50.330136153466 | | 1971 | 50.365813402526 | | 1970 | 50.397369488907 | | 1969 | 50.421072154025 | | 1968 | 50.438479526454 | | 1967 | 50.451206899542 | | 1966 | 50.460868603592 | | 1965 | 50.461283459603 | | 1964 | 50.455871731004 | | 1963 | 50.450353170437 | | 1962 | 50.444847822129 | | 1961 | 50.440745589562 | | 1960 | 50.4413527323 |
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