| Year | Value | | 2014 | 52.692486990665 | | 2013 | 51.173394982584 | | 2012 | 44.907642170336 | | 2011 | 46.656016611523 | | 2010 | 45.522489153009 | | 2009 | 44.115580009502 | | 2008 | 53.147877620413 | | 2007 | 53.28083683569 | | 2006 | 54.374885440297 | | 2005 | 54.652735588441 | | 2004 | 54.078090646489 | | 2003 | 50.744007928159 | | 2002 | 52.158724284323 | | 2001 | 53.256738538754 | | 2000 | 50.278499256835 | | 1999 | 49.403890844844 | | 1998 | 47.41289691104 | | 1997 | 45.856214727347 | | 1996 | 43.133287885119 | | 1995 | 43.08761901187 | | 1994 | 42.876312791676 | | 1993 | 44.06912254994 | | 1992 | 45.198326039972 | | 1991 | 42.068899997251 | | 1990 | 42.866147690104 | | 1989 | 41.714502842205 | | 1988 | 42.454736880266 | | 1987 | 46.27067537846 | | 1986 | 43.272390817534 | | 1985 | 41.10713141539 | | 1984 | 43.67602858288 | | 1983 | 41.165303216322 | | 1982 | 41.46291258898 | | 1981 | 42.435107460626 | | 1980 | 43.258648680163 | | 1979 | 42.325465127799 | | 1978 | 40.15527230273 | | 1977 | 40.466864000935 | | 1976 | 39.417863704752 | | 1975 | 38.565645314795 | | 1974 | 37.596595214677 | | 1973 | 36.404696626896 | | 1972 | 33.961178197488 | | 1971 | 33.561818681093 |
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