Year	%
1971	16.2
1973	15
1975	13.7
1977	14
1979	13.5
1981	12.7
1982	13
1984	13.7
1985	13.2
1986	12.2
1987	12.2
1988	11.2
1989	11.2
1990	12.2
1991	12.5
1992	12.5
1993	12.7
1994	12.2
1995	12.7
1996	13.2
1997	12.7
1998	13
1999	13.5
2000	13.2
2001	13.2
2002	13.2
2003	14
2004	13.7
2005	13.2
2006	12.7
2007	12.5
2008	13.5
2009	13.2
2010	13.2
2011	12.2
2012	14.2
2013	14.7
2014	13.7
2015	13.7
2016	12.7
2017	13.2
2018	12.2
2019	11.2