Year | Value | 2015 | 20.969042498326 | 2014 | 19.644325896656 | 2013 | 23.163554419538 | 2012 | 24.527138175798 | 2011 | 25.676573916797 | 2010 | 26.909432235019 | 2009 | 26.101109533851 | 2008 | 28.307389784363 | 2007 | 29.544985625845 | 2006 | 29.076069182202 | 2005 | 29.358731294816 | 2004 | 28.659226945228 | 2003 | 27.914397086407 | 2002 | 26.556011313704 | 2001 | 25.639087352988 | 2000 | 26.679741945323 | 1999 | 25.773222513691 | 1998 | 24.210661727305 | 1997 | 24.133431104373 | 1996 | 24.099659096496 | 1995 | 23.911303781975 | 1994 | 23.91418478159 | 1993 | 24.977241452195 | 1992 | 23.815032059717 | 1991 | 23.711154991721 | 1990 | 23.503703532803 | 1989 | 24.058574618858 | 1988 | 22.885127378831 | 1987 | 21.372076060835 | 1986 | 21.085351698505 | 1985 | 20.738009306327 | 1984 | 21.091266060693 | 1983 | 22.475126088614 | 1982 | 22.256062843726 | 1981 | 25.377479093002 | 1980 | 28.268550992049 | 1979 | 31.668407644402 | 1978 | 33.909283810965 | 1977 | 33.839656175565 | 1976 | 34.699041014975 | 1975 | 31.505651974634 | 1974 | 33.705896460681 | 1973 | 34.094802364751 | 1972 | 31.506032354022 | 1971 | 29.888826194125 | 1970 | 29.500019091911 | 1969 | 29.326784816325 | 1968 | 26.67112704951 | 1967 | 24.685404332634 | 1966 | 24.519813302689 | 1965 | 23.691339857821 | 1964 | 21.961508102703 | 1963 | 21.140441622018 | 1962 | 19.022630300248 | 1961 | 17.635803486572 | 1960 | 16.716146904006 |
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