Year | Value | 2021 | 14.3 | 2020 | 14.6 | 2019 | 15.2 | 2018 | 15 | 2017 | 15 | 2016 | 15.8 | 2015 | 15.6 | 2014 | 16.3 | 2013 | 16.6 | 2012 | 16.9 | 2011 | 16.2 | 2010 | 16.7 | 2009 | 16.7 | 2008 | 16.5 | 2007 | 17.1 | 2006 | 17.9 | 2005 | 17.4 | 2004 | 17.4 | 2003 | 18.2 | 2002 | 18.9 | 2001 | 19.9 | 2000 | 21.4 | 1999 | 20.6 | 1998 | 21.2 | 1997 | 22.3 | 1996 | 22.3 | 1995 | 21.9 | 1994 | 22.5 | 1993 | 23.5 | 1992 | 24.5 | 1991 | 25.7 | 1990 | 25.6 | 1989 | 23.6 | 1988 | 24.7 | 1987 | 25.7 | 1986 | 24.9 | 1985 | 23.4 | 1984 | 24.8 | 1983 | 25.8 | 1982 | 26.3 | 1981 | 27.7 | 1980 | 26.2 | 1979 | 26.3 | 1978 | 26.4 | 1977 | 28.8 | 1976 | 29 | 1975 | 31.1 | 1974 | 32 | 1973 | 33.3 | 1972 | 34.6 | 1971 | 34.8 | 1970 | 35 | 1969 | 35.1 | 1968 | 35.3 | 1967 | 35.4 | 1966 | 34.95 | 1965 | 34.5 | 1964 | 33.8 | 1963 | 33.1 | 1962 | 32.4 | 1961 | 33.2 | 1960 | 34 |
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