| Year | Value | | 2022 | 50.365509155557 | | 2021 | 50.380629516289 | | 2020 | 50.397842012193 | | 2019 | 50.411780024522 | | 2018 | 50.423503364693 | | 2017 | 50.434250775358 | | 2016 | 50.445095683027 | | 2015 | 50.454799867809 | | 2014 | 50.460105520737 | | 2013 | 50.463094620046 | | 2012 | 50.466400569188 | | 2011 | 50.469310273401 | | 2010 | 50.472254955252 | | 2009 | 50.476013269406 | | 2008 | 50.480914794048 | | 2007 | 50.484973169873 | | 2006 | 50.487629355932 | | 2005 | 50.489827670197 | | 2004 | 50.490677093202 | | 2003 | 50.490134315945 | | 2002 | 50.488809043872 | | 2001 | 50.486847956551 | | 2000 | 50.482718222136 | | 1999 | 50.477065297626 | | 1998 | 50.472298612219 | | 1997 | 50.466719101949 | | 1996 | 50.461770577741 | | 1995 | 50.459309587411 | | 1994 | 50.456704042858 | | 1993 | 50.454190498807 | | 1992 | 50.452098906401 | | 1991 | 50.44701193579 | | 1990 | 50.439447872994 | | 1989 | 50.43154539943 | | 1988 | 50.425564574636 | | 1987 | 50.421109147705 | | 1986 | 50.416520919753 | | 1985 | 50.41802628711 | | 1984 | 50.424641624656 | | 1983 | 50.430896804896 | | 1982 | 50.435766777768 | | 1981 | 50.436552992096 | | 1980 | 50.432674269988 | | 1979 | 50.431216637697 | | 1978 | 50.433082393445 | | 1977 | 50.432201388869 | | 1976 | 50.431217555963 | | 1975 | 50.429530190139 | | 1974 | 50.422007754172 | | 1973 | 50.410260086179 | | 1972 | 50.397587913749 | | 1971 | 50.390269969928 | | 1970 | 50.388673026827 | | 1969 | 50.384745535683 | | 1968 | 50.378366327223 | | 1967 | 50.372886904752 | | 1966 | 50.367755857311 | | 1965 | 50.362852709538 | | 1964 | 50.358538265863 | | 1963 | 50.351293468551 | | 1962 | 50.343533603912 | | 1961 | 50.341248317679 | | 1960 | 50.345353129158 |
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