| Year | Value | | 2014 | 44.433500881591 | | 2013 | 52.561530264946 | | 2012 | 59.701982077953 | | 2011 | 56.935425171038 | | 2010 | 49.245382043462 | | 2009 | 63.202884198649 | | 2008 | 66.657260145138 | | 2007 | 61.28845468583 | | 2006 | 75.338552009129 | | 2005 | 65.512923392299 | | 2004 | 70.285089286243 | | 2003 | 53.891750146058 | | 2002 | 51.245427653301 | | 2001 | 55.372357393766 | | 2000 | 66.757538837908 | | 1999 | 71.568351770595 | | 1998 | 58.393968553669 | | 1997 | 63.743258700984 | | 1996 | 65.42976176116 | | 1995 | 60.6012370932 | | 1994 | 50.97672233126 | | 1993 | 52.617578635001 | | 1992 | 53.273027248569 | | 1991 | 55.398108284142 | | 1990 | 48.974103492744 | | 1989 | 62.679960205676 | | 1988 | 56.409995517114 | | 1987 | 43.438033516167 | | 1986 | 40.1034569244 | | 1985 | 44.221239593636 | | 1984 | 43.765793363212 | | 1983 | 46.714942213922 | | 1982 | 59.796624726849 | | 1981 | 67.089516881494 | | 1980 | 71.013026102142 | | 1979 | 79.166698895491 | | 1978 | 76.609362030236 | | 1977 | 76.619711614386 | | 1976 | 78.357131313343 | | 1975 | 78.702483229134 | | 1974 | 77.679638394044 | | 1973 | 77.465167590252 | | 1972 | 80.001794504108 | | 1971 | 78.498212739265 |
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