| Year | Value | | 2022 | 50.340290479687 | | 2021 | 50.349133585734 | | 2020 | 50.356077673516 | | 2019 | 50.363297587723 | | 2018 | 50.37521299047 | | 2017 | 50.389100785588 | | 2016 | 50.401698490745 | | 2015 | 50.408347120782 | | 2014 | 50.418826721098 | | 2013 | 50.440545453274 | | 2012 | 50.464954291669 | | 2011 | 50.490818638809 | | 2010 | 50.517941775721 | | 2009 | 50.550591168175 | | 2008 | 50.583134384918 | | 2007 | 50.61282436933 | | 2006 | 50.642619208978 | | 2005 | 50.670047966713 | | 2004 | 50.698673238493 | | 2003 | 50.727300977168 | | 2002 | 50.748465394022 | | 2001 | 50.760602555412 | | 2000 | 50.766504657275 | | 1999 | 50.775576115906 | | 1998 | 50.791918930831 | | 1997 | 50.802888385989 | | 1996 | 50.794122661014 | | 1995 | 50.783822701757 | | 1994 | 50.835295238013 | | 1993 | 50.82601589136 | | 1992 | 50.78328111111 | | 1991 | 50.808943545718 | | 1990 | 50.822505517623 | | 1989 | 50.834388317763 | | 1988 | 50.832953959149 | | 1987 | 50.835467815639 | | 1986 | 50.8564759627 | | 1985 | 50.877663487485 | | 1984 | 50.90403918164 | | 1983 | 50.935490190851 | | 1982 | 50.97064036429 | | 1981 | 51.002339701916 | | 1980 | 51.050724419257 | | 1979 | 51.103134621748 | | 1978 | 51.138210778307 | | 1977 | 51.179677896068 | | 1976 | 51.219990973375 | | 1975 | 51.261298313895 | | 1974 | 51.308021350633 | | 1973 | 51.339707961752 | | 1972 | 51.266220476951 | | 1971 | 51.207765342386 | | 1970 | 51.246457093161 | | 1969 | 51.279994416587 | | 1968 | 51.313791296198 | | 1967 | 51.35307969814 | | 1966 | 51.396420968642 | | 1965 | 51.430951973199 | | 1964 | 51.471455591267 | | 1963 | 51.52498208188 | | 1962 | 51.569129022047 | | 1961 | 51.619795935471 | | 1960 | 51.668737084163 |
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