| Year | Value | | 2022 | 49.713227642774 | | 2021 | 49.706239013339 | | 2020 | 49.698573880681 | | 2019 | 49.689228788058 | | 2018 | 49.675073495281 | | 2017 | 49.66079679161 | | 2016 | 49.645855842496 | | 2015 | 49.625955910548 | | 2014 | 49.600447528406 | | 2013 | 49.571212822634 | | 2012 | 49.538499803741 | | 2011 | 49.503768494274 | | 2010 | 49.469348510713 | | 2009 | 49.431137849463 | | 2008 | 49.3921830119 | | 2007 | 49.35689417329 | | 2006 | 49.321514603697 | | 2005 | 49.283653139244 | | 2004 | 49.241133215957 | | 2003 | 49.200030879387 | | 2002 | 49.159183673469 | | 2001 | 49.115381101739 | | 2000 | 49.065464352281 | | 1999 | 49.025246489394 | | 1998 | 48.998842086865 | | 1997 | 48.970487110823 | | 1996 | 48.943416097165 | | 1995 | 48.913323799029 | | 1994 | 48.878482228626 | | 1993 | 48.841572950759 | | 1992 | 48.802159203415 | | 1991 | 48.760004654831 | | 1990 | 48.714227011837 | | 1989 | 48.627879957331 | | 1988 | 48.502731174405 | | 1987 | 48.374489125154 | | 1986 | 48.236475001465 | | 1985 | 48.087801140333 | | 1984 | 47.932980681127 | | 1983 | 47.77384155338 | | 1982 | 47.607234056308 | | 1981 | 47.433553649276 | | 1980 | 47.25870882562 | | 1979 | 47.833437369954 | | 1978 | 48.691001470785 | | 1977 | 48.798830549145 | | 1976 | 48.635384133433 | | 1975 | 48.454073130085 | | 1974 | 48.256908593987 | | 1973 | 48.050414371858 | | 1972 | 47.847055142577 | | 1971 | 47.64800213818 | | 1970 | 47.460899343822 | | 1969 | 47.287492590397 | | 1968 | 47.126507055342 | | 1967 | 46.992220499048 | | 1966 | 46.878939502242 | | 1965 | 46.761385701086 | | 1964 | 46.637606389582 | | 1963 | 46.508522727273 | | 1962 | 46.37744732494 | | 1961 | 46.239956666968 | | 1960 | 46.093363051015 |
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