| Year | Value | | 2022 | 49.659045873037 | | 2021 | 49.635110820965 | | 2020 | 49.614504087635 | | 2019 | 49.596785666476 | | 2018 | 49.585374670824 | | 2017 | 49.575404295024 | | 2016 | 49.533136555587 | | 2015 | 49.476172375537 | | 2014 | 49.436117751418 | | 2013 | 49.39210844414 | | 2012 | 49.339298011015 | | 2011 | 49.290656962688 | | 2010 | 49.247043919189 | | 2009 | 49.207443882238 | | 2008 | 49.150333163662 | | 2007 | 49.067171897176 | | 2006 | 49.007640123558 | | 2005 | 48.974084043274 | | 2004 | 48.94288167252 | | 2003 | 48.914289424694 | | 2002 | 48.884831676855 | | 2001 | 48.866972122126 | | 2000 | 48.866710785862 | | 1999 | 48.854190264678 | | 1998 | 48.839280601996 | | 1997 | 48.836827666665 | | 1996 | 48.839475445249 | | 1995 | 48.848364881448 | | 1994 | 48.854372242559 | | 1993 | 48.852867474486 | | 1992 | 48.847061890866 | | 1991 | 48.853392290924 | | 1990 | 48.838646225326 | | 1989 | 48.796396381215 | | 1988 | 48.770172210929 | | 1987 | 48.75525884287 | | 1986 | 48.74303608749 | | 1985 | 48.729007156918 | | 1984 | 48.711120743174 | | 1983 | 48.697801154273 | | 1982 | 48.683748524476 | | 1981 | 48.661299293734 | | 1980 | 48.646685064818 | | 1979 | 48.645781996274 | | 1978 | 48.656616242614 | | 1977 | 48.679244501967 | | 1976 | 48.708044367616 | | 1975 | 48.743938997837 | | 1974 | 48.778081557531 | | 1973 | 48.811919913891 | | 1972 | 48.84113197681 | | 1971 | 48.849060818436 | | 1970 | 48.852711605641 | | 1969 | 48.8461166807 | | 1968 | 48.818447764775 | | 1967 | 48.783595840953 | | 1966 | 48.746093024662 | | 1965 | 48.709323998937 | | 1964 | 48.670131183693 | | 1963 | 48.619236634358 | | 1962 | 48.553491907473 | | 1961 | 48.485503091629 | | 1960 | 48.446260167225 |
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