Year	%
1979	16.1
1986	16.2
1992	16.3
1997	15.9
2001	15.8
2002	15.9
2003	15.6
2004	15.6
2005	15.2
2006	15.6
2007	15.7
2008	15.5
2009	15.5
2010	15.5
2011	15.6
2012	15.8
2013	16
2014	16.3
2015	16.2
2016	16.4
2017	16.6
2018	16.5
2019	16.6
2020	16.6
2021	16.6