Year | Value | 2021 | 8.793 | 2020 | 8.004 | 2019 | 8.04 | 2018 | 8.337 | 2017 | 8.69 | 2016 | 9.049 | 2015 | 9.506 | 2014 | 10.005 | 2013 | 10.492 | 2012 | 10.995 | 2011 | 11.473 | 2010 | 11.902 | 2009 | 12.149 | 2008 | 12.536 | 2007 | 12.93 | 2006 | 13.399 | 2005 | 13.753 | 2004 | 14.073 | 2003 | 14.434 | 2002 | 14.731 | 2001 | 15.181 | 2000 | 15.677 | 1999 | 16.217 | 1998 | 16.829 | 1997 | 17.321 | 1996 | 17.91 | 1995 | 18.429 | 1994 | 18.853 | 1993 | 19.144 | 1992 | 19.515 | 1991 | 19.812 | 1990 | 20.036 | 1989 | 20.313 | 1988 | 20.57 | 1987 | 22.614 | 1986 | 22.76 | 1985 | 24.664 | 1984 | 24.964 | 1983 | 23.276 | 1982 | 23.482 | 1981 | 23.761 | 1980 | 21.891 | 1979 | 21.897 | 1978 | 21.787 | 1977 | 21.794 | 1976 | 21.791 | 1975 | 21.796 | 1974 | 22.149 | 1973 | 22.392 | 1972 | 22.501 | 1971 | 22.478 | 1970 | 22.533 | 1969 | 22.618 | 1968 | 22.682 | 1967 | 22.73 | 1966 | 22.79 | 1965 | 22.801 | 1964 | 22.871 | 1963 | 22.701 | 1962 | 22.778 | 1961 | 22.928 | 1960 | 23.183 |
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