| Year | Value | | 2009 | 67.672035139092 | | 2008 | 72.733753118688 | | 2007 | 71.82196826271 | | 2006 | 71.042861964225 | | 2005 | 72.306710006965 | | 2004 | 68.959446333171 | | 2003 | 64.404508552061 | | 2002 | 63.396537510305 | | 2001 | 63.223772214791 | | 2000 | 64.371670941014 | | 1999 | 64.309833213957 | | 1998 | 63.863963664562 | | 1997 | 63.974077074413 | | 1996 | 63.188893563315 | | 1995 | 64.212999216915 | | 1994 | 63.422818791946 | | 1993 | 60.717230008244 | | 1992 | 60.990230905862 | | 1991 | 60.294920808301 | | 1990 | 56.624825662483 | | 1989 | 59.497098646035 | | 1988 | 68.342458934793 | | 1987 | 68 | | 1986 | 61.39846743295 | | 1985 | 57.871396895787 | | 1984 | 68.531468531469 | | 1983 | 58.640776699029 | | 1982 | 56.190476190476 | | 1981 | 69.098712446352 | | 1980 | 68.90243902439 | | 1979 | 56.944444444444 |
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