| Year | Value | | 2022 | 50.655206035127 | | 2021 | 50.671654818701 | | 2020 | 50.686780274183 | | 2019 | 50.701636952822 | | 2018 | 50.717628913436 | | 2017 | 50.733117197189 | | 2016 | 50.745033038787 | | 2015 | 50.755208224177 | | 2014 | 50.763173533328 | | 2013 | 50.774625519549 | | 2012 | 50.791859794453 | | 2011 | 50.808524833441 | | 2010 | 50.829884548438 | | 2009 | 50.854732726999 | | 2008 | 50.886409147179 | | 2007 | 50.920999751211 | | 2006 | 50.944813240406 | | 2005 | 50.968453229331 | | 2004 | 51.000166477269 | | 2003 | 51.050844391514 | | 2002 | 51.104135000691 | | 2001 | 51.152207193796 | | 2000 | 51.187522984855 | | 1999 | 51.065637390053 | | 1998 | 50.855816352406 | | 1997 | 50.783330664119 | | 1996 | 50.799863785311 | | 1995 | 50.851373527039 | | 1994 | 50.91241126071 | | 1993 | 50.952272083794 | | 1992 | 50.993491929065 | | 1991 | 51.017251694275 | | 1990 | 51.032670375263 | | 1989 | 51.036543393347 | | 1988 | 51.034585624695 | | 1987 | 51.03319160849 | | 1986 | 51.03510392586 | | 1985 | 51.035228246201 | | 1984 | 51.028874444878 | | 1983 | 51.023439088706 | | 1982 | 51.015308001793 | | 1981 | 51.010717876451 | | 1980 | 51.010565856565 | | 1979 | 51.000013012531 | | 1978 | 50.97979688046 | | 1977 | 50.954437240898 | | 1976 | 50.92497865279 | | 1975 | 50.895430111788 | | 1974 | 50.87339550813 | | 1973 | 50.868061104993 | | 1972 | 50.870425808338 | | 1971 | 50.871130287529 | | 1970 | 50.87016440018 | | 1969 | 50.868235525512 | | 1968 | 50.863424498306 | | 1967 | 50.855238505401 | | 1966 | 50.847892309939 | | 1965 | 50.84097102802 | | 1964 | 50.831960747394 | | 1963 | 50.820907059435 | | 1962 | 50.807928936817 | | 1961 | 50.793661719761 | | 1960 | 50.777400238333 |
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