| Year | Value | | 2021 | 54.710446106955 | | 2020 | 54.710446106955 | | 2019 | 54.710446106955 | | 2018 | 54.710446106955 | | 2017 | 54.710446106955 | | 2016 | 54.710446106955 | | 2015 | 54.710446106955 | | 2014 | 54.710446106955 | | 2013 | 54.705597118315 | | 2012 | 53.153920753671 | | 2011 | 55.661263507897 | | 2010 | 54.452479911333 | | 2009 | 52.659600997506 | | 2008 | 51.430174563591 | | 2007 | 50.203934607925 | | 2006 | 55.83097811028 | | 2005 | 52.812690495982 | | 2004 | 52.268356885564 | | 2003 | 49.413549459684 | | 2002 | 44.750346356331 | | 2001 | 41.583818232197 | | 2000 | 38.930451648656 | | 1999 | 38.847326129122 | | 1998 | 38.9165973954 | | 1997 | 38.9165973954 | | 1996 | 38.930451648656 | | 1995 | 38.930451648656 | | 1994 | 38.930451648656 | | 1993 | 38.944305901912 | | 1992 | 38.999722914935 | | 1991 | 39.138265447492 | | 1990 | 39.138265447492 | | 1989 | 39.138265447492 | | 1988 | 39.138265447492 | | 1987 | 39.124411194237 | | 1986 | 39.055139927958 | | 1985 | 38.985868661679 | | 1984 | 38.293155998892 | | 1983 | 38.085342200055 | | 1982 | 38.016070933777 | | 1981 | 37.80825713494 | | 1980 | 37.738985868662 | | 1979 | 37.669714602383 | | 1978 | 37.531172069825 | | 1977 | 37.392629537268 | | 1976 | 37.323358270989 | | 1975 | 37.25408700471 | | 1974 | 37.184815738432 | | 1973 | 37.115544472153 | | 1972 | 37.046273205874 | | 1971 | 36.977001939596 | | 1970 | 36.907730673317 | | 1969 | 36.838459407038 | | 1968 | 36.769188140759 | | 1967 | 36.630645608202 | | 1966 | 36.561374341923 | | 1965 | 36.492103075644 | | 1964 | 36.422831809365 | | 1963 | 36.353560543087 | | 1962 | 36.256580770297 | | 1961 | 36.187309504018 |
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