| Year | Value | | 2022 | 50.057148370032 | | 2021 | 50.059443374231 | | 2020 | 50.061993899169 | | 2019 | 50.064847839593 | | 2018 | 50.072467470505 | | 2017 | 50.081564809481 | | 2016 | 50.089341762898 | | 2015 | 50.100308309833 | | 2014 | 50.112652307112 | | 2013 | 50.123237751928 | | 2012 | 50.137134469858 | | 2011 | 50.153919448822 | | 2010 | 50.171613318419 | | 2009 | 50.194586620878 | | 2008 | 50.221855329687 | | 2007 | 50.250623747418 | | 2006 | 50.283676468004 | | 2005 | 50.320691976969 | | 2004 | 50.360004425613 | | 2003 | 50.401018730949 | | 2002 | 50.440387396815 | | 2001 | 50.47913386831 | | 2000 | 50.526861580776 | | 1999 | 50.572504217414 | | 1998 | 50.596561447327 | | 1997 | 50.55653196811 | | 1996 | 50.530906999409 | | 1995 | 50.57643030016 | | 1994 | 50.624077445846 | | 1993 | 50.672739776298 | | 1992 | 50.72119408574 | | 1991 | 50.762983273365 | | 1990 | 50.796102178429 | | 1989 | 50.822554725232 | | 1988 | 50.842306695495 | | 1987 | 50.855914182872 | | 1986 | 50.864973412404 | | 1985 | 50.872097956176 | | 1984 | 50.879160569884 | | 1983 | 50.879242319214 | | 1982 | 50.873598188775 | | 1981 | 50.868519251125 | | 1980 | 50.861989792571 | | 1979 | 50.85431418317 | | 1978 | 50.845663965403 | | 1977 | 50.834583200727 | | 1976 | 50.821175224478 | | 1975 | 50.806955355137 | | 1974 | 50.802073050345 | | 1973 | 50.806393184641 | | 1972 | 50.810692168583 | | 1971 | 50.814875301963 | | 1970 | 50.818080886822 | | 1969 | 50.819761613751 | | 1968 | 50.819903808894 | | 1967 | 50.820456977639 | | 1966 | 50.820052233447 | | 1965 | 50.817450878408 | | 1964 | 50.813569974171 | | 1963 | 50.80780675652 | | 1962 | 50.800109318307 | | 1961 | 50.790774862451 | | 1960 | 50.779630062906 |
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