Year | Value | 2021 | 18.2241246138 | 2020 | 18.2241246138 | 2019 | 16.53964984552 | 2018 | 16.53964984552 | 2017 | 16.77973738414 | 2016 | 16.501029866117 | 2015 | 16.542224510814 | 2014 | 16.658084449022 | 2013 | 18.363800205973 | 2012 | 18.331616889804 | 2011 | 18.2736869207 | 2010 | 18.17070030896 | 2009 | 17.424047373841 | 2008 | 18.247940267765 | 2007 | 17.59140061792 | 2006 | 17.784500514933 | 2005 | 17.572090628218 | 2004 | 17.964727085479 | 2003 | 17.958290422245 | 2002 | 17.835993820803 | 2001 | 17.855303810505 | 2000 | 18.434603501545 | 1999 | 18.724253347065 | 1998 | 18.531153450052 | 1997 | 18.312306900103 | 1996 | 18.312306900103 | 1995 | 18.292996910402 | 1994 | 18.215756951596 | 1993 | 19.2263130793 | 1992 | 18.717816683831 | 1991 | 18.717816683831 | 1990 | 18.724253347065 | 1989 | 18.730690010299 | 1988 | 18.898043254377 | 1987 | 19.181256436663 | 1986 | 19.503089598352 | 1985 | 19.760556127703 | 1984 | 20.082389289392 | 1983 | 20.211122554068 | 1982 | 20.339855818744 | 1981 | 20.404222451081 | 1980 | 20.539392378991 | 1979 | 21.923274974253 | 1978 | 21.96833161689 | 1977 | 22.702111225541 | 1976 | 22.399588053553 | 1975 | 21.949021627189 | 1974 | 21.498455200824 | 1973 | 21.176622039135 | 1972 | 20.790422245108 | 1971 | 20.597322348095 | 1970 | 20.552265705458 | 1969 | 20.507209062822 | 1968 | 20.468589083419 | 1967 | 20.468589083419 | 1966 | 20.468589083419 | 1965 | 20.468589083419 | 1964 | 20.468589083419 | 1963 | 19.953656024717 | 1962 | 19.953656024717 | 1961 | 19.953656024717 |
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