Year	%
2000	20.1
2001	19.6
2002	19.1
2003	18.7
2004	18.1
2005	17.7
2006	17.3
2007	17.3
2008	17.1
2009	17
2010	16.9
2011	17.1
2012	16.9
2013	17.1
2014	17.3
2015	17.5
2016	17.7
2017	17.5
2018	17.5
2019	17.5