Year % 1963 11.4 1964 11.3 1965 11.4 1966 11.3 1967 11.5 1968 11.7 1969 11.7 1970 11.6 1971 11.6 1972 11.6 1973 11.8 1974 12 1975 11.9 1976 11.9 1977 11.9 1978 12.1 1979 12 1980 12 1981 11.8 1982 11.5 1983 11.3 1984 11.3 1985 11.2 1986 11.2 1987 11.3 1988 11.1 1989 11 1990 11 1991 11.1 1992 11 1993 10.5 1994 10.6 1995 10.7 1996 10.5 1997 10.5 1998 10.7 1999 10.7 2000 10.7 2001 10.6 2002 10.6 2003 10.5 2004 10.7 2005 10.5 2006 10.4 2007 10.5 2008 10.5 2009 10.5 2010 10.6 2011 10.3 2012 10.3 2013 10.4 2014 10.2 2015 10.3 2016 10.3 2017 10.2 2018 10.3 2019 10.2 2020 10.6 2021 10.6