Year	%
1971	16.3
1973	16.8
1975	16.8
1977	17
1979	17
1981	16.9
1982	16.9
1984	16.9
1985	17
1986	17.3
1987	17.2
1988	17.2
1989	17.4
1990	17.5
1991	17.3
1992	17.3
1993	17.4
1994	17.4
1995	17.4
1996	17.1
1997	17
1998	16.9
1999	17
2000	16.9
2001	16.9
2002	16.9
2003	16.8
2004	16.8
2005	16.9
2006	16.7
2007	16.6
2008	16.7
2009	16.7
2010	16.8
2011	17
2012	17.1
2013	17
2014	17
2015	16.9
2016	17.1
2017	17
2018	17
2019	17.2