| Year | Value | | 2015 | 64.175546638785 | | 2014 | 61.970670223049 | | 2013 | 60.119869276217 | | 2012 | 60.751623727613 | | 2011 | 64.020470221328 | | 2010 | 65.823226035074 | | 2009 | 65.771479769235 | | 2008 | 67.587401780882 | | 2007 | 66.342618781556 | | 2006 | 66.689330193525 | | 2005 | 65.894639619807 | | 2004 | 65.314081525894 | | 2003 | 66.008786379526 | | 2002 | 63.882913383277 | | 2001 | 64.41668939573 | | 2000 | 63.13240619694 | | 1999 | 62.932120592426 | | 1998 | 61.624972155324 | | 1997 | 60.71296902228 | | 1996 | 61.031293001252 | | 1995 | 58.998978939593 | | 1994 | 59.295788707786 | | 1993 | 58.950349063353 | | 1992 | 59.566173548189 | | 1991 | 58.202486720579 | | 1990 | 57.09855527608 | | 1989 | 58.056337690703 | | 1988 | 56.79897714707 | | 1987 | 55.073914305166 | | 1986 | 56.6934984869 | | 1985 | 60.503840536339 | | 1984 | 60.721804781595 | | 1983 | 62.227127484718 | | 1982 | 63.379003535072 | | 1981 | 69.842189248631 | | 1980 | 75.331321587999 | | 1979 | 75.332358200531 | | 1978 | 75.77994795921 | | 1977 | 73.565687350275 | | 1976 | 72.862738040527 | | 1975 | 75.075890271153 | | 1974 | 78.272798122462 | | 1973 | 80.235843094019 | | 1972 | 78.510790700026 | | 1971 | 76.007855365714 | | 1970 | 78.00220165755 | | 1969 | 83.674547692685 | | 1968 | 84.78480942479 | | 1967 | 84.840181765848 | | 1966 | 83.7817321132 | | 1965 | 84.338156726652 | | 1964 | 85.90700356878 | | 1963 | 84.12544410647 | | 1962 | 86.982581615607 | | 1961 | 87.39548763575 | | 1960 | 86.615201150666 |
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