Year	%
1979	17.4
1986	18
1991	17.8
1995	17.7
2000	17.2
2003	17.3
2004	16.4
2005	16.6
2006	18
2007	17.5
2008	17.7
2009	17.9
2010	18
2011	18.2
2012	18.1
2013	17.9
2014	17.9
2015	17.7
2016	17.6
2017	18
2018	17.8
2019	17.7