| Year | Value | | 2022 | 51.274841502073 | | 2021 | 51.329205270264 | | 2020 | 51.373128899362 | | 2019 | 51.392857430317 | | 2018 | 51.381879749061 | | 2017 | 51.360894634519 | | 2016 | 51.332765181879 | | 2015 | 51.302835305509 | | 2014 | 51.261468887246 | | 2013 | 51.20950304913 | | 2012 | 51.159311222204 | | 2011 | 51.115398967881 | | 2010 | 51.072734848836 | | 2009 | 51.038718442205 | | 2008 | 51.022449647 | | 2007 | 51.011784544795 | | 2006 | 51.003666956426 | | 2005 | 50.972861741575 | | 2004 | 50.938435317592 | | 2003 | 50.92787003457 | | 2002 | 50.92316017316 | | 2001 | 50.87539075013 | | 2000 | 50.82408303875 | | 1999 | 50.79334165817 | | 1998 | 50.740632830255 | | 1997 | 50.690325947716 | | 1996 | 50.633813019123 | | 1995 | 50.608117229784 | | 1994 | 50.615468952457 | | 1993 | 50.618891684473 | | 1992 | 50.62836163849 | | 1991 | 50.640891766303 | | 1990 | 50.600340769927 | | 1989 | 50.526989487445 | | 1988 | 50.48828125 | | 1987 | 50.456066108141 | | 1986 | 50.421879119913 | | 1985 | 50.410745337891 | | 1984 | 50.41323578928 | | 1983 | 50.400024952824 | | 1982 | 50.378709687664 | | 1981 | 50.354747474747 | | 1980 | 50.334632397678 | | 1979 | 50.323713927227 | | 1978 | 50.352308080383 | | 1977 | 50.419073696865 | | 1976 | 50.494113745648 | | 1975 | 50.569427276473 | | 1974 | 50.643938772497 | | 1973 | 50.65348691376 | | 1972 | 50.590544576049 | | 1971 | 50.530451866405 | | 1970 | 50.474432856869 | | 1969 | 50.419004332079 | | 1968 | 50.393615679775 | | 1967 | 50.400072740498 | | 1966 | 50.400529139413 | | 1965 | 50.426614774343 | | 1964 | 50.479920141289 | | 1963 | 50.541551792044 | | 1962 | 50.607982548275 | | 1961 | 50.674262040394 | | 1960 | 50.74427197248 |
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