| Year | Value | | 2021 | 70.23 | | 2020 | 71.37 | | 2019 | 73.18 | | 2018 | 73.15 | | 2017 | 72.95 | | 2016 | 72.41 | | 2015 | 71.97 | | 2014 | 71.44 | | 2013 | 70.62 | | 2012 | 69.52 | | 2011 | 68.69 | | 2010 | 68.45 | | 2009 | 68.39 | | 2008 | 67.11 | | 2007 | 66.34 | | 2006 | 66.15 | | 2005 | 65.86 | | 2004 | 66.06 | | 2003 | 65.74 | | 2002 | 65.95 | | 2001 | 65.76 | | 2000 | 65.45 | | 1999 | 65.63 | | 1998 | 64.5 | | 1997 | 64 | | 1996 | 63.6 | | 1995 | 63.5 | | 1994 | 64.9 | | 1993 | 65.4 | | 1992 | 67.4 | | 1991 | 67.6 | | 1990 | 68.336585365854 | | 1989 | 68.290243902439 | | 1988 | 68.848780487805 | | 1987 | 69.290243902439 | | 1986 | 68.913414634146 | | 1985 | 68.536585365854 | | 1984 | 68.536585365854 | | 1983 | 67.662195121951 | | 1982 | 66.787804878049 | | 1981 | 66.706097560976 | | 1980 | 66.624390243902 | | 1979 | 62.254585365854 | | 1978 | 62.065609756098 | | 1977 | 61.853 | | 1976 | 61.640341463415 | | 1975 | 61.790609756098 | | 1974 | 61.524975609756 | | 1973 | 61.277390243902 | | 1972 | 60.994951219512 | | 1971 | 60.64756097561 | | 1970 | 60.422975609756 | | 1969 | 60.191170731707 | | 1968 | 59.998365853658 | | 1967 | 59.873414634146 | | 1966 | 59.699219512195 | | 1965 | 59.461682926829 | | 1964 | 59.157487804878 | | 1963 | 58.944512195122 | | 1962 | 58.621756097561 | | 1961 | 58.503073170732 | | 1960 | 58.370512195122 |
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