| Year | Value | | 2021 | 79 | | 2020 | 80.1 | | 2019 | 81.2 | | 2018 | 80.7 | | 2017 | 80.5 | | 2016 | 80.1 | | 2015 | 79.7 | | 2014 | 80.1 | | 2013 | 79.6 | | 2012 | 79.6 | | 2011 | 79.3 | | 2010 | 78.8 | | 2009 | 78.6 | | 2008 | 77.6 | | 2007 | 77.2 | | 2006 | 77.1 | | 2005 | 77.4 | | 2004 | 77.8 | | 2003 | 77.9 | | 2002 | 77.6 | | 2001 | 77.6 | | 2000 | 77.5 | | 1999 | 77 | | 1998 | 76.7 | | 1997 | 76.62 | | 1996 | 75.86 | | 1995 | 75.04 | | 1994 | 74.82 | | 1993 | 74.98 | | 1992 | 75.93 | | 1991 | 75.86 | | 1990 | 76.17 | | 1989 | 76.24 | | 1988 | 76.29 | | 1987 | 76.36 | | 1986 | 76.46 | | 1985 | 75.49 | | 1984 | 75.57 | | 1983 | 75.91 | | 1982 | 76.01 | | 1981 | 75.68 | | 1980 | 75.64 | | 1979 | 75.64 | | 1978 | 75.45 | | 1977 | 75.66 | | 1976 | 75.87 | | 1975 | 75.6 | | 1974 | 75.69 | | 1973 | 75.65 | | 1972 | 75.45 | | 1971 | 76.13 | | 1970 | 75.03 | | 1969 | 74.98 | | 1968 | 75.15 | | 1967 | 75.43 | | 1966 | 75.08 | | 1965 | 74.68 | | 1964 | 74.91 | | 1963 | 73.8 | | 1962 | 72.44 | | 1961 | 73.56 | | 1960 | 72.9 |
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