Year | Value | 2022 | 14.3 | 2021 | 17.5 | 2020 | 15.5 | 2019 | 13.4 | 2018 | 13.6 | 2017 | 13.4 | 2016 | 13.1 | 2015 | 13.2 | 2014 | 12.8 | 2013 | 12.4 | 2012 | 12.7 | 2011 | 12.5 | 2010 | 12.8 | 2009 | 12.6 | 2008 | 12.3 | 2007 | 12.1 | 2006 | 12.2 | 2005 | 12.3 | 2004 | 12.1 | 2003 | 12.4 | 2002 | 12.4 | 2001 | 11.7 | 2000 | 11.4 | 1999 | 11.8 | 1998 | 12 | 1997 | 12.4 | 1996 | 12.7 | 1995 | 12 | 1994 | 11.7 | 1993 | 11.6 | 1992 | 11.6 | 1991 | 10.9 | 1990 | 10.6 | 1989 | 10.7 | 1988 | 11 | 1987 | 11.1 | 1986 | 10.6 | 1985 | 10.9 | 1984 | 10.3 | 1983 | 10.4 | 1982 | 10 | 1981 | 10 | 1980 | 10.4 | 1979 | 9.8 | 1978 | 9.7 | 1977 | 9.6 | 1976 | 9.5 | 1975 | 9.3 | 1974 | 9.1 |
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