Year	%
1963	23.1
1964	23
1965	23.2
1966	23.3
1967	23.2
1968	23.2
1969	23.2
1970	23.2
1971	23.1
1972	23.3
1973	23.3
1974	23.4
1975	23.4
1976	23.4
1977	23.3
1978	23.5
1979	23.4
1980	23.5
1981	23.5
1982	23.6
1983	23.7
1984	23.6
1985	23.5
1986	23.6
1987	23.7
1988	23.5
1989	23.2
1990	23.3
1991	23.3
1992	23.3
1993	22.8
1994	22.6
1995	22.6
1996	22.5
1997	22.3
1998	22.5
1999	22.5
2000	22.3
2001	22.2
2002	22.5
2003	22.6
2004	22.5
2005	22.3
2006	22.2
2007	22.4
2008	22.5
2009	22.4
2010	22.9
2011	22.6
2012	22.6
2013	22.6
2014	22.4
2015	22.4
2016	22.5
2017	22.7
2018	22.5
2019	22.5
2020	22.6
2021	22.1