Year | Value | 2021 | 13.1 | 2020 | 12.3 | 2019 | 12.3 | 2018 | 12 | 2017 | 11.9 | 2016 | 12 | 2015 | 12.5 | 2014 | 13.4 | 2013 | 13.4 | 2012 | 14.1 | 2011 | 14.1 | 2010 | 15.4 | 2009 | 15.8 | 2008 | 15.2 | 2007 | 14.6 | 2006 | 14.5 | 2005 | 14.4 | 2004 | 14.5 | 2003 | 14.3 | 2002 | 14.1 | 2001 | 14.4 | 2000 | 15.3 | 1999 | 14.8 | 1998 | 15.2 | 1997 | 15.3 | 1996 | 16.1 | 1995 | 16 | 1994 | 16.7 | 1993 | 17.5 | 1992 | 17.7 | 1991 | 17.6 | 1990 | 18.7 | 1989 | 18 | 1988 | 18.7 | 1987 | 16.6 | 1986 | 16.4 | 1985 | 16 | 1984 | 17.2 | 1983 | 18.4 | 1982 | 18.5 | 1981 | 18.8 | 1980 | 19.8 | 1979 | 19.8 | 1978 | 18.6 | 1977 | 18 | 1976 | 19.5 | 1975 | 20.1 | 1974 | 19.9 | 1973 | 21.7 | 1972 | 22.4 | 1971 | 20.8 | 1970 | 19.7 | 1969 | 20.7 | 1968 | 21 | 1967 | 22.2 | 1966 | 24 | 1965 | 24.6 | 1964 | 25.3 | 1963 | 26 | 1962 | 25.8 | 1961 | 25.5 | 1960 | 28 |
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