Year | Value | 2021 | 16.7 | 2020 | 14.6 | 2019 | 12.3 | 2018 | 12.5 | 2017 | 12.4 | 2016 | 12.9 | 2015 | 13 | 2014 | 13.1 | 2013 | 13 | 2012 | 13.3 | 2011 | 13.5 | 2010 | 14.2 | 2009 | 14.1 | 2008 | 14.5 | 2007 | 14.6 | 2006 | 15.1 | 2005 | 16.1 | 2004 | 15.9 | 2003 | 16.4 | 2002 | 16.2 | 2001 | 15.6 | 2000 | 15.3 | 1999 | 14.6 | 1998 | 13.5 | 1997 | 13.8 | 1996 | 14.2 | 1995 | 15 | 1994 | 15.7 | 1993 | 14.5 | 1992 | 12.2 | 1991 | 11.4 | 1990 | 11.2 | 1989 | 10.7 | 1988 | 10.7 | 1987 | 10.5 | 1986 | 10.4 | 1985 | 11.3 | 1984 | 11.6 | 1983 | 11.1 | 1982 | 10.7 | 1981 | 10.9 | 1980 | 11 | 1979 | 10.8 | 1978 | 10.435 | 1977 | 10.217 | 1976 | 10.098 | 1975 | 9.841 | 1974 | 9.373 | 1973 | 9.281 | 1972 | 9.137 | 1971 | 8.916 | 1970 | 8.808 | 1969 | 8.725 | 1968 | 8.261 | 1967 | 8.076 | 1966 | 7.803 | 1965 | 7.72 | 1964 | 7.395 | 1963 | 7.643 | 1962 | 7.833 | 1961 | 7.59 | 1960 | 7.594 |
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