Year	%
1987	17.9
1992	18.2
1995	18.2
2000	18.1
2003	17.9
2004	18
2005	17.9
2006	17.7
2007	17.6
2008	18
2009	17.9
2010	17.6
2011	17.5
2012	17.4
2013	17.3
2014	17.3
2015	17.2
2016	17.4
2017	17.2
2018	17.3
2019	17.3
2020	17.5
2021	17.3