Year | Value | 2015 | 12.519211097017 | 2014 | 12.22014084507 | 2013 | 13.498064932273 | 2012 | 12.384904759061 | 2011 | 14.008635402232 | 2010 | 14.130076247306 | 2009 | 15.661360583381 | 2008 | 15.320524846455 | 2007 | 15.349852309345 | 2006 | 15.829512708434 | 2005 | 14.068635097493 | 2004 | 13.835977745724 | 2003 | 13.349940119761 | 2002 | 13.407759303246 | 1997 | 15.964648364047 | 1996 | 17.462946817786 | 1995 | 17.623039215686 | 1994 | 19.047428571429 | 1993 | 18.764175257732 | 1992 | 18.480230050323 | 1991 | 14.737777777778 | 1990 | 13.234864300626 | 1989 | 13.838961038961 | 1988 | 14.349025974026 | 1987 | 14.570873786408 | 1986 | 16.319727891157 | 1985 | 17.254691689008 | 1984 | 18.446202531646 | 1983 | 21.082706766917 | 1982 | 21.695760598504 | 1981 | 26.244299694152 | 1979 | 21.285197869102 | 1978 | 23.071096644762 | 1977 | 25.51797220429 | 1976 | 17.331384422635 | 1975 | 20.521614593148 |
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