Year	%
1985	17.7
1986	17.5
1987	17.4
1988	17.3
1989	16.5
1990	17.5
1991	17.7
1992	17.4
1993	17.5
1994	17.5
1995	17.4
1996	17.4
1997	17.2
1998	17.1
1999	17.2
2000	17.1
2001	16.8
2002	16.8
2003	17.2
2004	17.2
2005	17.1
2006	17.1
2007	17
2008	16.7
2009	17.2
2010	17.3
2011	17
2012	16.5
2013	17
2014	17.2
2015	16.8
2016	17.1
2017	16.7
2018	16.5
2019	16.5
2020	16.8
2021	17.3