Year | Value | 2021 | 12.8 | 2020 | 12.9 | 2019 | 13.2 | 2018 | 13.4 | 2017 | 13.1 | 2016 | 13.6 | 2015 | 12.4 | 2014 | 13.2 | 2013 | 13 | 2012 | 12.9 | 2011 | 12 | 2010 | 13.2 | 2009 | 12.6 | 2008 | 13.8 | 2007 | 14 | 2006 | 13.7 | 2005 | 14.7 | 2004 | 14.8 | 2003 | 14.7 | 2002 | 15 | 2001 | 13.6 | 2000 | 15.1 | 1999 | 13.9 | 1998 | 14 | 1997 | 15.1 | 1996 | 15.5 | 1995 | 14.8 | 1994 | 15 | 1993 | 16.6 | 1992 | 17.2 | 1991 | 18.3 | 1990 | 19.9 | 1989 | 19.5 | 1988 | 18.4 | 1987 | 16.8 | 1986 | 17.2 | 1985 | 16.3 | 1984 | 15.4 | 1983 | 15.4 | 1982 | 16.4 | 1981 | 17.2 | 1980 | 17.1 | 1979 | 18.4 | 1978 | 17.5 | 1977 | 18.2 | 1976 | 18.3 | 1975 | 19.2 | 1974 | 19.9 | 1973 | 20.5 | 1972 | 20.5 | 1971 | 20.2 | 1970 | 21.1 |
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