Year	%
1968	9.9
1969	9.5
1970	9.5
1971	9.1
1972	8.9
1973	9.3
1974	9.1
1975	9.3
1976	9.4
1977	9.5
1978	9.3
1979	9.4
1980	9.1
1981	8.7
1982	8.6
1983	8.7
1984	8.7
1985	8.5
1986	8.1
1987	7.7
1988	7.7
1989	7.6
1990	7.1
1991	7.2
1992	7.1
1993	7
1994	7
1995	7.1
1996	7.1
1997	7
1998	6.9
1999	6.8
2000	6.7
2001	6.9
2002	7.2
2003	7.3
2004	7.3
2005	7.1
2006	7.1
2007	7.2
2008	7.1
2009	7.2
2010	7.5
2011	7.6
2012	7.6
2013	7.7
2014	7.5
2015	7.5
2016	7.4
2017	7.5
2018	7.3
2019	7.3
2020	7.6
2021	7.6