Year | Value | 2014 | 24.123168782688 | 2013 | 23.438585082514 | 2012 | 22.811166743198 | 2011 | 23.116467007606 | 2010 | 23.560466763245 | 2009 | 23.355858638103 | 2008 | 24.099555589446 | 2007 | 24.204010562281 | 2006 | 22.987470599077 | 2005 | 20.285170988362 | 2004 | 20.781303947169 | 2003 | 20.074558650501 | 2002 | 24.228320558571 | 2001 | 24.914686713244 | 2000 | 26.80658374726 | 1999 | 27.696748959642 | 1998 | 26.678714471791 | 1997 | 27.023284450868 | 1996 | 25.490667865019 | 1995 | 23.335280984805 | 1994 | 22.898463377306 | 1993 | 20.872995163199 | 1992 | 19.492264997413 | 1991 | 17.772686043138 | 1990 | 20.331510090385 | 1989 | 19.303278958273 | 1988 | 19.212997707508 | 1987 | 18.304523831013 | 1986 | 18.296903584712 | 1985 | 19.411083567595 | 1984 | 20.290215770328 | 1983 | 18.949991201032 | 1982 | 17.852318335629 | 1981 | 16.834411632823 | 1980 | 15.49814769378 | 1979 | 16.253898153133 | 1978 | 15.170330079003 | 1977 | 14.999546992906 | 1976 | 15.70743833324 | 1975 | 16.062462659144 | 1974 | 15.787659833339 | 1973 | 15.140069038659 | 1972 | 15.260158142527 | 1971 | 15.744547482099 |
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