Year	%
1963	16.3
1964	16.1
1965	16.3
1966	16.3
1967	16.4
1968	16.5
1969	16.6
1970	16.5
1971	16.4
1972	16.6
1973	16.7
1974	16.8
1975	16.8
1976	16.8
1977	16.8
1978	17
1979	16.9
1980	17
1981	16.8
1982	16.6
1983	16.6
1984	16.5
1985	16.4
1986	16.5
1987	16.6
1988	16.4
1989	16.2
1990	16.2
1991	16.3
1992	16.2
1993	15.7
1994	15.7
1995	15.7
1996	15.5
1997	15.5
1998	15.7
1999	15.7
2000	15.6
2001	15.5
2002	15.6
2003	15.5
2004	15.7
2005	15.4
2006	15.4
2007	15.5
2008	15.5
2009	15.5
2010	15.7
2011	15.4
2012	15.4
2013	15.4
2014	15
2015	15.1
2016	15.3
2017	15.3
2018	15.3
2019	15.2
2020	15.6
2021	15.3